- Address review feedback: introduce NO_REF_PART symbolic name, better comments

Analysis:
A query with implicit grouping is one with aggregate functions and
no GROUP BY clause. MariaDB inherits from MySQL an SQL extenstion
that allows mixing aggregate functions with non-aggregate fields.
If a query with such mixed select clause produces an empty result
set, the meaning of aggregate functions is well defined - either
NULL (MIN, MAX, etc.), or 0 (count(*)). However the non-aggregated
fields must also have some value, and the only reasonable value in
the case of empty result is NULL.

The cause of the many wrong results was that if a field is declared
as non-nullable (e.g. because it is a PK or NOT NULL), the semantic
analysis and the optimization phases treat this field as non-nullable,
and generate all related query plan elements based on this assumption.

Later during execution, these incorrectly configured/generated query
plan elements result in a wrong result because the selected fields
are not null due to the not-null assumption during optimization.

Solution:
Detect before the context analysys phase that a query uses implicit
grouping with mixed aggregates/non-aggregates, and set all fields
as nullable. The parser already walks the SELECT clause, and
already sets Item::with_sum_func for Items that reference aggreagate
functions. The patch adds a symmetric Item::with_field so that all
Items that reference an Item_field are marked during their
construction at parse time in the same way as with aggregate function
use.

Changed test suite to use --log-basename (to get the code tested)
Added --sync-sys=1 to test suite to speed it up.
Better error messages if something goes wrong with mysql_install_db


mysql-test/Makefile.am:
  Removed not existing directory
mysql-test/lib/My/ConfigFactory.pm:
  Use log-basename
  We had to also set 'log_error' as some test was explicitely using the old name
  Added 'sync-sys=1' to speed up test suite
mysql-test/r/variables-notembedded.result:
  Updated test results (variable relay_log is now set)
mysql-test/suite/binlog/t/binlog_delete_and_flush_index-master.opt:
  Force specific names for some log files.
mysql-test/suite/binlog/t/binlog_index-master.opt:
  Force specific names for some log files.
mysql-test/suite/binlog/t/binlog_stm_unsafe_warning-master.opt:
  Force specific names for some log files.
mysql-test/suite/binlog/t/binlog_stm_unsafe_warning.test:
  Better error message if something goes wrong
mysql-test/suite/rpl/r/rpl_flushlog_loop.result:
  Updated results
mysql-test/suite/rpl/rpl_1slave_base.cnf:
  Use --log-basename
scripts/mysql_install_db.sh:
  More information to --help
  Write url to knowledge base if something goes wrong
  Fail at once if we can't create a database directory (no reason to continue and write a screenful of not related text)
scripts/mysqld_safe.sh:
  Also allow one to use --data for --datadir (common shortening)
  Added support for --log-basename
  Fail at once if we can't create a log directory
  Fixed bug where we used a pid file name without '.pid' extension
sql/log.cc:
  Create a log file name trough my_once_alloc()  (To get it automaticly freed at exit)
sql/mysql_priv.h:
  Added new prototype
sql/mysqld.cc:
  Added support for --log-basename
  Better help for a lot of log-filename related variables.
sql/rpl_rli.cc:
  Write information that one can use --log-basename
sql/set_var.cc:
  Add log_basename as a readonly variable

Ensure that all clients reads the appropriate 'client', client-mariadb and 'mariadb' sections from my.cnf
The mysqld server and all clients now reads the new client-server section
Fixed that mysqldumpslow supports new slow log formats and new mysqld --slow- options


client/mysql.cc:
  Read also client-server and client-mariadb sections.
client/mysql_upgrade.c:
  Read also client-server and client-mariadb sections.
client/mysqladmin.cc:
  Read also client-server and client-mariadb sections.
client/mysqlbinlog.cc:
  Read also client-server and client-mariadb sections.
client/mysqlcheck.c:
  Read also client-server and client-mariadb sections.
client/mysqldump.c:
  Read also client-server and client-mariadb sections.
client/mysqlimport.c:
  Read also client-server and client-mariadb sections.
client/mysqlshow.c:
  Read also client-server and client-mariadb sections.
client/mysqltest.cc:
  Read also client-server and client-mariadb sections.
extra/my_print_defaults.c:
  Updated help text
scripts/mysql_fix_privilege_tables.sh:
  Read also sections client client-server client-mariadb
scripts/mysql_install_db.pl.in:
  Also allow --data=* option
  Read also groups mariadb, server and client-server.
scripts/mysql_install_db.sh:
  Also allow --data=* option
  Read also groups mariadb, server and client-server.
  Added --lose-skip-pbxt to bootstrap
scripts/mysql_secure_installation.sh:
  Read also groups client-server and client-mariadb
scripts/mysqld_multi.sh:
  Read also group mariadb
scripts/mysqld_safe.sh:
  Read also groups mariadb server and client-server
scripts/mysqldumpslow.sh:
  Fixed to support new slow log formats
  Added sorting on -ae (aggregated number of retreived rows) and e (retrieved rows)
  Read also group 'mariadb'
  If there is many instances of same option, use last one.
  Get slow log file from options log-slow-queries=filename or query-log-file=filename
  Added support for future --log-basename option
sql-common/client.c:
  Read also groups 'client-server' and 'client-mariadb'
tests/mysql_client_test.c:
  Read also groups 'client-server' and 'client-mariadb'
tests/thread_test.c:
  Read also groups 'client-server' and 'client-mariadb'

after Monty's review.

Analysis (BUG#719198):
The assert failed because the execution code for
partial matching is designed with the assumption that
NULLs on the left side are detected as early as possible,
and a NULL result is returned before any lookups are
performed at all.

However, in the case of an Item_cache object on the left
side, null was not detected properly, because detection
was done via Item::is_null(), which is not implemented at
all for Item_cache, and resolved to the default Item::is_null()
which always returns FALSE.

Solution:
Imlpement Item::is_null().

******

Analysis (BUG#730604):
The method Item_field::is_null() determines if an item is NULL from its
Item_field::field object. However, for Item_fields that represent internal
temporary tables, Item_field::field represents the field of the original
table that was the source for the temporary table (in this case t1.f3).
Both in the committed test case, and in the original bug report the current
value of t1.f3 is not NULL. This results in an incorrect count of NULLs
for this column. As a consequence, all related Ordered_key buffers are
allocated with incorrect sizes. Depending on the exact query and data,
these incorrect sizes result in various crashes or failed asserts.

Solution:
The correct value of the current field of the internal temp table is
in Item_field::result_field. This value is determined by
Item::is_null_result().

Do not reset the value of the item_equal field in the Item_field object
once it has been set.

Address Monty's review comments

Added item.real_type() for easy access to the underlaying types for Item_ref and Item_cache_wrapper()
This allows us to simplify and speed up some tests and also remove get_cached_item()

sql/item.h:
  Added item.real_type()
  Removed get_cached_item()
sql/opt_range.cc:
  Simplify test
sql/sql_select.cc:
  Simplify test
sql/sql_show.cc:
  Simplify test

Analysis:
The assert failed because the execution code for
partial matching is designed with the assumption that
NULLs on the left side are detected as early as possible,
and a NULL result is returned before any lookups are
performed at all.

However, in the case of an Item_cache object on the left
side, null was not detected properly, because detection
was done via Item::is_null(), which is not implemented at
all for Item_cache, and resolved to the default Item::is_null()
which always returns FALSE.

Solution:
Use the property Item::null_value instead of is_null(), which
is properly updated for Item_cache objects as well.

Don't check if LAST_IO_Error has changed as this is not a user variable and it may change depending on timing issues between master and slave

If join condition is of the form <t2.key>=<t1.no_key> then the server
performs no index look-ups when looking for matching rows of t2 for
the rows from t1 with t1.no_key=NULL. It happens because the function
add_not_null_conds() injects an additional condition of the form 
IS NOT NULL(<t1.no_key>) into the WHERE condition.
However if the join condition was of the form <t.key>=<outer_ref> no
additional null rejecting predicate was generated. This could lead
to extra records in the result set if the value of <outer_ref> happened
to be NULL.
The new code injects null rejecting predicates of the form 
IS NOT NULL(<outer_ref>) and evaluates them before the first row
the subquery is constructed.

- put the code that sets HA_NULL_PART bit back
- Fix test_if_ref/part_of_refkey() so that 
  = NULL-ability of lookup columns does not prevent the equality 
    from being removed (we now have early/late NULLs filtering which 
    will filter out NULL values)
  = equality is not removed if it is ref_or_null access, and the value 
    of the lookup column can alternate between the lookup value and NULL.

Generally, we should use only small letters for table names 
but here it's easier to fix with one --replace.

- cleaner code
- ability to change from using pointers to offsets at some point