The bug could caused a crash when the server executed a query with
ORDER by and sort_buffer_size was set to a small enough number.
It happened because the small sort buffer did not allow to allocate
all merge buffers in it.
Made sure that the allocated sort buffer would be big enough
to contain all possible merge buffers.  

Following reasons caused mismatches:
  - different handling of invalid values;
  - different CAST results with fractional seconds;
  - microseconds support in MariaDB;
  - different algorithm of comparing temporal values;
  - differences in error and warning texts and codes;
  - different approach to truncating datetime values to time;
  - additional collations;
  - different record order for queries without ORDER BY;
  - MySQL bug#66034.
More details in MDEV-369 comments.

Following reasons caused mismatches:
  - different handling of invalid values;
  - different CAST results with fractional seconds;
  - microseconds support in MariaDB;
  - different algorithm of comparing temporal values;
  - differences in error and warning texts and codes;
  - different approach to truncating datetime values to time;
  - additional collations;
  - different record order for queries without ORDER BY;
  - MySQL bug#66034.
More details in MDEV-369 comments.

- index_merge/intersection is unable to work on GIS indexes, because:
  1. index scans have no Rowid-Ordered-Retrieval property
  2. When one does an index-only read over a GIS index, they do not 
     get the index tuple, because index only contains bounding box of the geometry.
     This is why key_copy() call crashed.
This patch fixes #1, which makes the problem go away. Theoretically, it would 
be nice to check #2, too, but SE API semantics is not sufficiently precise to do it.

TABLE_LIST::check_single_table made aware about fact that now if table attached to a merged view it can be (unopened) temporary table
(in 5.2 it was always leaf table or non (in case of several tables)).

The bug was the result of the incomplete fix for bug lp bug 1008293.

We set correct cmp_context during preparation to avoid changing it later by Item_field::equal_fields_propagator.
(see mysql bugs #57135 #57692 during merging)

- put back the result encoding in func_in.result (messed up by kdiff3)
- update .result for other tests (checked)

Virtual columns of ENUM and SET data types were not supported properly
in the original patch that introduced virtual columns into MariaDB 5.2.
The problem was that for any  virtual column the patch used the 
interval_id field of the definition of the column in the frm file as
a reference to the virtual column expression.
The fix stores the optional interval_id of the virtual column in the
extended header of the virtual column expression. 

Analysis:
The fix for bug lp:985667 implements the method Item_subselect::no_rows_in_result()
for all main kinds of subqueries. The purpose of this method is to be called from
return_zero_rows() and set Items to some default value in the case when a query
returns no rows. Aggregates and subqueries require special treatment in this case.

Every implementation of Item_subselect::no_rows_in_result() called
Item_subselect::make_const() to set the subquery predicate to its default value
irrespective of where the predicate was located in the query. Once the predicate
was set to a constant it was never executed.

At the same time, the JOIN object of the fake select for UNIONs (the one used for
the final result of the UNION), was set after all subqueries in the union were
executed. Since we set the subquery as constant, it was never executed, and the
corresponding JOIN was never created.

In order to decide whether the result of NOT IN is NULL or FALSE, Item_in_optimizer
needs to check if the subquery result was empty or not. This is where we got the
crash, because subselect_union_engine::no_rows() checks for
unit->fake_select_lex->join->send_records, and the join object was NULL.

Solution:
If a subquery is in the HAVING clause it must be evaluated in order to know its
result, so that we can properly filter the result records. Once subqueries in the
HAVING clause are executed even in the case of no result rows, this specific
crash will be solved, because the UNION will be executed, and its JOIN will be
constructed. Therefore the fix for this crash is to narrow the fix for lp:985667,
and to apply Item_subselect::no_rows_in_result() only when the subquery predicate
is in the SELECT clause.

Analysis:
Queries with implicit grouping (there is aggregate, but no group by)
follow some non-obvious semantics in the case of empty result set.
Aggregate functions produce some special "natural" value depending on
the function. For instance MIN/MAX return NULL, COUNT returns 0.

The complexity comes from non-aggregate expressions in the select list.
If the non-aggregate expression is a constant, it can be computed, so
we should return its value, however if the expression is non-constant,
and depends on columns from the empty result set, then the only meaningful
value is NULL.

The cause of the wrong result was that for subqueries the optimizer didn't
make a difference between constant and non-constant ones in the case of
empty result for implicit grouping.

Solution:
In all implementations of Item_subselect::no_rows_in_result() check if the
subquery predicate is constant. If it is constant, do not set it to the
default value for implicit grouping, instead let it be evaluated.

One of the reported problems manifested itself in the scenario when one
thread tried to to get statistics on a key cache while the second thread
had not finished initialization of the key cache structure yet. 
The problem was resolved by forcing serialization of such operations
on key caches.

To serialize function calls to perform certain operations over a key cache
a new mutex associated with the key cache now is used. It is stored in the
field op_lock of the KEY_CACHE structure. It is locked when the operation
is performed. Some of the serialized key cache operations utilize calls 
for other key cache operations. To avoid recursive locking of op_lock
the new functions that perform the operations of key cache initialization,
destruction and re-partitioning with an additional parameter were introduced.
The parameter says whether the operation over op_lock are to be performed or
are to be omitted. The old functions for the operations of key cache 
initialization, destruction,and  re-partitioning  now just call the
corresponding new functions with the additional parameter set to true
requesting to use op_lock while all other calls of these new function
have this parameter set to false. 

Another problem reported in the bug entry concerned the operation of
assigning an index to a key cache. This operation can be called
while the key cache structures are not initialized yet. In this
case any call of flush_key_blocks() should return without any actions.

No test case is provided with this patch.

- Add the VIA_SYM token into keyword_sp list, which makes it allowed for
  use as keyword and SP label.

LP1008334 : Speedup specific datetime queries that got slower with introduction of microseconds in 5.3

- Item::get_seconds() now skips decimal arithmetic, if decimals is 0. This significantly speeds up from_unixtime() if no fractional part is passed.
- replace sprintfs used to format temporal values  by hand-coded formatting 
  
Query1 (original query in the bug report)
BENCHMARK(10000000,DATE_SUB(FROM_UNIXTIME(RAND() * 2147483648), INTERVAL (FLOOR(1 + RAND() * 365)) DAY)) 
  
Query2 (Variation of query1 that does not use fractional part in FROM_UNIXTIME parameter)
BENCHMARK(10000000,DATE_SUB(FROM_UNIXTIME(FLOOR(RAND() * 2147483648)), INTERVAL (FLOOR(1 + RAND() * 365)) DAY)) 
  
Prior to the patch, the runtimes were (32 bit compilation/AMD machine)
Query1: 41.53 sec 
Query2: 23.90 sec
  
With the patch, the runtimes are
Query1: 32.32 sec (speed up due to removing sprintf)
Query2: 12.06 sec (speed up due to skipping decimal arithmetic)

Analysis:

When the method JOIN::choose_subquery_plan() decided to apply
the IN-TO-EXISTS strategy, it set the unit and select_lex
uncacheable flag to UNCACHEABLE_DEPENDENT_INJECTED unconditionally.
As result, even if IN-TO-EXISTS injected non-correlated predicates,
the subquery was still treated as correlated.

Solution:
Set the subquery as correlated only if the injected predicate(s) depend
on the outer query.

remove the offending assert.
take the test case from mysql Bug#58015

- Set index columns to be read when using index_merge, even if TABLE->no_keyread is 
  set for the table (happens for multi-table UPDATEs)

with false condition, gets confused and throws wrong errors

The constructor for Query_log_event allocated 2 bytes too few for
extra space needed by Query cache. (Not sure if this is reproducible
in practice, as there are often a couple of extra bytes allocated
for unused string zero terminators, but better safe than sorry).

Analysis:

When a subquery that needs a temp table is executed during
the prepare or optimize phase of the outer query, at the end
of the subquery execution all the JOIN_TABs of the subquery
are replaced by a new JOIN_TAB that selects from the temp table.
However that temp table has no corresponding TABLE_LIST.
Once EXPLAIN execution reaches its last phase, it tries to print
the names of the subquery tables through its TABLE_LISTs, but in
the case of this bug there is no such TABLE_LIST (it is NULL),
hence a crash.

Solution:
The fix is to block subquery evaluation inside
Item_func_like::fix_fields and Item_func_like::select_optimize()
using the Item::is_expensive() test.

        Optimizator fails using index with ST_Within(g, constant_poly).

per-file comments:
  mysql-test/r/gis-rt-precise.result
        test result fixed.
  mysql-test/r/gis-rtree.result
        test result fixed.
  mysql-test/suite/maria/r/maria-gis-rtree-dynamic.result
        test result fixed.
  mysql-test/suite/maria/r/maria-gis-rtree-trans.result
        test result fixed.
  mysql-test/suite/maria/r/maria-gis-rtree.result
        test result fixed.
  storage/maria/ma_rt_index.c
        Use MBR_INTERSECT mode when optimizing the select WITH ST_Within.
  storage/myisam/rt_index.c
        Use MBR_INTERSECT mode when optimizing the select WITH ST_Within.

The problem is that some fix_fields do not call Item_func::fix_fields and do not collect with subselect_information.