A fix of unions with duplicate rows and returning bug fix for lp:732124 union + limit returns wrong result

Fixed type and testing of last_update type for innodb_table_stats

mysql-test/r/connect.result:
  Removed tables which are not created anymore
sql/item_sum.h:
  Fixed typo
sql/sql_base.cc:
  Don't update table and index statics for temporary tables
sql/sys_vars.cc:
  Merge
storage/innobase/dict/dict0stats.cc:
  Fixed type last_update to TIMESTAMP.

Disabled some asserts that we can't yet have enabled

- temporary tables now works
- mysql-system_tables updated to not use temporary tables
- PASSWORD() function fixed
- Support for STATS_AUTO_RECALC, STATS_PERSISTENT and STATS_SAMPLE_PAGES table options

Error processing in mysql_create_table() fixed.

- mdl.cc and mdl.h merged completely
- mysql_system_tables*.sql merged completely
- Fixed wrong merge of lock_tables
- Added some missing functions:
 - bool THD::notify_shared_lock()
 - Dynamic_array::pop, Dynamic_array::del
- Added MDL_context_owner to THD
- Added metadata_locks_hash_instances

  committer: Sergei Golubchik <sergii@pisem.net> 
    fix for a valgrind builds. 
    my_alloca() cannot have MY_THREAD_SPECIFIC, because can be used 
    outside of the THD context. 

MDEV-537 Make multi-column non-top level subqueries to be executed via index (index/unique subquery)
           instead of single_select_engine

This task changes the IN-EXISTS rewrite for multi-column subqueries
"(a, b) IN (select b, c ...)" to work in the same way as for
single-column subqueries "a IN (select b ...) with respect to the
injection of NULL-rejecting predicates.
 
More specifically, the method
Item_in_subselect::create_row_in_to_exists_cond()
adds Item_is_not_null_test and Item_func_trig_cond only if the left
IN operand can be NULL. Not having these predicates when not necessary,
makes it possible to rewrite the subquery into a "unique_subquery" or
"index_subquery" when there is a suitable index on the only
subquery table.

otherwise safemalloc and my_malloc_size_cb_func will use
current_thd before it's defined

MDEV-3997: Querying a Cassandra table on a server with query cache enabled is likely to cause problems
- Disable query cache for Cassandra tables.

my_alloca() cannot have MY_THREAD_SPECIFIC, because can be used
outside of the THD context.

when no ha_example.so is built

Add a wait for binlog checkpoint to avoid thread scheduling
giving different binlog order at random.

When CHANGE MASTER fails, it may or may not have already added
the Master_info * to the index. Implement logic that properly
handles removal and freeing in both cases.

to storage/cassandra/CMakeLists.txt

storage/cassandra/CMakeLists.txt:
  more thourough CHECK_CXX_SOURCE_COMPILES test, that checks whether
  boost::shared_ptr can work with --fno-rtti
  
  don't install anything in INSTALL_SYSCONFDIR, if the latter is unset