fixed error code in union test


mysql-test/t/union.test:
  right code worr 4.1 error
sql/log_event.cc:
  assign non-cachable for Item status for all stack tables for safety
sql/repl_failsafe.cc:
  assign non-cachable for Item status for all stack tables for safety
sql/slave.cc:
  assign non-cachable for Item status for all stack tables for safety
sql/sql_acl.cc:
  assign non-cachable for Item status for all stack tables for safety
sql/sql_base.cc:
  assign non-cachable for Item status for all stack tables for safety
  non-cachable status processing
sql/sql_cache.cc:
  assign non-cachable for Item status for all stack tables for safety
sql/sql_class.cc:
  removed ald way to prevent using stack tables for caching Items in PS
sql/sql_class.h:
  removed old way to prevent using stack tables for caching Items in PS
sql/sql_help.cc:
  assign non-cachable for Item status for all stack tables for safety
sql/sql_insert.cc:
  assign non-cachable for Item status for all stack tables for safety
  removed old way to prevent using stack tables for caching Items in PS
sql/table.h:
  non-cachable for Item status for tables