Fortify wsrep_hton so that wsrep calls are not done to NULL-pointers.

        Implementing the 'IF EXISTS' option for statements
        ALTER TABLE ALTER COLUMN SET/DROP DEFAULT.

- Galera tests that was not updated with connection change
  messages
- Test where out of memory error was changed (We are now using the
  standard out of memory error in most places)
- Removed tokudb tests that uses include files that doesn't exist
  in MariaDB
- Removed not supported mariadb startup option from option file

- Galera tests that was not updated with connection change
  messages
- Disabled some TokuDB tests that always timed out.
  These should be enabled again when we have an option to
  specicy timeouts per tests.

Do not apply splitting for constant tables.

Do not SET DEBUG_DBUG=-d,... in tests. To disable debug instrumentation,
save and restore the original value of the variable DEBUG_DBUG.
Assigning -d,... will enable the output of a lot of unrelated DBUG
messages to the server error log.

rx_i_s_cache_t is now bool, not ibool.

The patch for MDEV-15107 fixed this problem. Adding tests only.

Tests started to fail after a merge of MDEV-15107 (from bb-10.2-ext to 10.3),
because MDEV-15107 additionally fixed this problem:
  MDEV-15112 Inconsistent evaluation of spvariable=0 in strict mode

Modifying tests not to reply on the pre-MDEV-15112 behavior.

This reverts commit 3486135b.

The commit comment ended in the words: "This is needed later."
Apparently the "later" never arrived.

Remove unnecessary repeated lookups for undo pages.

trx_undo_assign(), trx_undo_assign_low(), trx_undo_seg_create(),
trx_undo_create(): Return the undo log block to the caller.

Inside InnoDB, each mini-transaction that generates any redo log records
will acquire log_sys->mutex during mtr_t::commit() in order to copy the
records into the global log_sys->buf for writing into the redo log file.

For single-row transactions, this incurs quite a bit of overhead.
We would use two mini-transactions for writing a record into a
freshly updated undo log page. (Only if the undo record will
not fit in that page, then we will have to commit and restart
the mini-transaction.)

trx_undo_assign(): Assign undo log for a persistent transaction,
or return the already assigned one.

trx_undo_assign_low(): Assign undo log for an operation on a
persistent or temporary table.

trx_undo_create(), trx_undo_reuse_cached(): Remove redundant parameters.
Merge the logic from trx_undo_mark_as_dict_operation().

Removed not used have_semisync_plugin.inc

MDEV-15107 Add virtual Field::sp_prepare_and_store_item(), make sp_rcontext symmetric for scalar and ROW

After MDEV-14212, the Virtual_tmp_table instance that stores a ROW
variable elements is accessible from the underlying Field_row
(rather than Item_field_row).

This patch makes some further changes by moving the code from
sp_instr_xxx, sp_rcontext, Item_xxx to Virtual_tmp_table and Field_xxx.

The data type specific code (scalar vs ROW) now resides in
a new virtual method Field_xxx::sp_prepare_and_store_item().
The the code in sp_rcontext::set_variable() and sp_eval_expr()
is now symmetric for scalar and ROW values.
The code in sp_rcontext::set_variable_row_field(), sp_rcontext::set_variable_row_field(), sp_rcontext::set_variable_row()
is now symmetric for ROW elements (i.e. scalar and ROW elements inside a ROW).

Rationale:

Prepare the code to implement these tasks soon easier:

- MDEV-12252 ROW data type for stored function return values
- MDEV-12307 ROW data type for built-in function return values
- MDEV-6121 Data type: Array
- MDEV-10593 sql_mode=ORACLE: TYPE .. AS OBJECT: basic functionality
- ROW with ROW fields (no MDEV yet)

Details:

1. Moving the code in sp_eval_expr() responsible to backup/restore
   thd->count_cuted_fields, thd->abort_on_warning,
   thd->transaction.stmt.modified_non_trans_table
   into a new helper class Sp_eval_expr_state, to reuse it easier.
   Fixing sp_eval_expr() to use this new class.

2. Moving sp_eval_expr() and sp_prepare_func_item() from public functions
   to methods in THD, so they can be reused in *.cc files easier without
   a need to include "sp_head.h".

   Splitting sp_prepare_func_item() into two parts.
   Adding a new function sp_fix_func_item(), which fixes
   the underlying items, but does not do check_cols() for them.
   Reusing sp_fix_func_item() in Field_row::sp_prepare_and_store_item().

3. Moving the code to find ROW fields by name from Item to Virtual_tmp_table

   Moving the code searching for ROW fields by their names
   from Item_field_row::element_index_by_name() to a new method
   Item_field_row to Virtual_tmp_table::sp_find_field_by_name().

   Adding wrapper methods sp_rcontext::find_row_field_by_name() and
   find_row_field_by_name_or_error(), to search for a ROW variable
   fields by the variable offset and its field name.

   Changing Item_splocal_row_field_by_name::fix_fields() to do
   use sp_rcontext::find_row_field_by_name_or_error().
   Removing virtual Item::element_index_by_name().

4. Splitting sp_rcontext::set_variable()

   Adding a new virtual method Field::sp_prepare_and_store_item().
   Spliting the two branches of the code in sp_rcontext::set_variable()
   into two virtual implementations of Field::sp_prepare_and_store_item(),
   (for Field and for Field_row).

   Moving the former part of sp_rcontext::set_variable() with the loop
   doing set_null() for all ROW fields into a new method
   Virtual_tmp_table::set_all_fields_to_null() and using it in
   Field_row::sp_prepare_and_store_item().

   Moving the former part of sp_rcontext::set_variable() with the loop
   doing set_variable_row_field() into a new method
   Virtual_tmp_table::set_all_fields_from_item() and using it in
   Field_row::sp_prepare_and_store_item().
   The loop in the new method now uses sp_prepare_and_store_item()
   instead of set_variable_row_field(), because saving/restoring
   THD flags is now done on the upper level. No needs to save/restore
   on every iteration.

5. Fixing sp_eval_expr() to simply do two things:
   - backup/restore THD flags
   - call result_field->sp_prepare_and_store_item()
   So now sp_eval_expr() can be used for both scalar and ROW variables.
   Reusing it in sp_rcontext::set_variable*().

6. Moving the loop in sp_rcontext::set_variable_row() into a
   new method Virtual_tmp_table::sp_set_all_fields_from_item_list().

   Changing the loop body to call field->sp_prepare_and_store_item()
   instead of doing set_variable_row_field(). This removes
   saving/restoring of the THD flags from every interation.
   Instead, adding the code to save/restore the flags around
   the entire loop in set_variable_row(), using Sp_eval_expr_state.
   So now saving/restoring is done only once for the entire ROW
   (a slight performance improvement).

7. Removing the code in sp_instr_set::exec_core() that sets
   a variable to NULL if the value evaluation failed.
   sp_rcontext::set_variable() now makes sure to reset
   the variable properly by effectively calling sp_eval_expr(),
   which calls virtual Field::sp_prepare_and_store_item().

   Removing the similar code from sp_instr_set_row_field::exec_core()
   and sp_instr_set_row_field_by_name::exec_core().

   Removing the method sp_rcontext::set_variable_row_field_to_null(),
   as it's not used any more.

8. Removing the call for sp_prepare_func_item() from
   sp_rcontext::set_variable_row_field(), as it was duplicate:
   it was done inside sp_eval_expr(). Now it's done inside
   virtual Field::sp_prepare_and_store_item().

9. Moving the code from sp_instr_set_row_field_by_name::exec_core()
   into sp_rcontext::set_variable_row_field_by_name(), for symmetry
   with other sp_instr_set*::exec_core()/sp_rcontext::set_variable*() pairs.
   Now sp_instr_set_row_field_by_name::exec_core() calls
   sp_rcontext::set_variable_row_field_by_name().

10. Misc:
   - Adding a helper private method sp_rcontext::virtual_tmp_table_for_row(),
     reusing it in a new sp_rcontext methods.
   - Removing Item_field_row::get_row_field(), as it's not used any more.
   - Removing the "Item *result_item" from sp_eval_expr(),
     as it's not needed any more.

Solve 3 way deadlock between plugin_initialiaze(), THD::init() and
mysql_sys_var_char().

The deadlock exists because of the lock order inversion between
LOCK_global_system_variables mutex and LOCK_system_variables_hash
read-write lock-

In this case, it is enough to change LOCK_system_variables_hash to prefer
reads to fix the deadlock, i.e change it to mysql_prlock_t

        Now we don't open partitions if it was explicitly cpecified.
        ha_partition::m_opened_partition bitmap added to track
        partitions that were actually opened.

Only invoke set_versioned() on trx_id versioned tables.

dict_table_t::versioned_by_id(): New accessor, to determine if
a table is system versioned by transaction ID.

One can use -DTRASH_FREED_MEMORY to enable TRASH
macros. Useful to do when one suspects that there
is accesses to freed memory.

Extended my_free() to TRASH freed memory

Conflicts:
	sql/table.cc

Only warnings, should not have caused any bugs in old code

I disabled rocksdb in ASAN build as I got a link error when
it's included

           replicate_events_marked_for_skip=FILTER_ON_MASTER

When events of a big transaction are binlogged offsetting over 2GB from
the beginning of the log the semisync master's dump thread
lost such events.
The events were skipped by the Dump thread that found their skipping
status erroneously.

The current fixes make sure the skipping status is computed correctly.
The test verifies them simulating the 2GB offset.

do not include test suite in release zip anymore.