sql/mysql_priv.h:
  description moved to be accessable from sql_class.h
sql/sql_base.cc:
  put all derived table preparation in temporary memory pull
sql/sql_class.h:
  close tables to close derived tables before freeing memory pool where they are placed
sql/sql_prepare.cc:
  now temporary memory pool for prrepared statements registration is oppened in open_and_lock_tables
  thd->current_statement set only for tables preparation, because we do not need memory pool tricks for PS executing
tests/client_test.c:
  derived table added to test
  expression with aggregate functions added to test