mysql-test/r/union.result:
  fix for union test becuase now not all fields in UNION allow NULLS
  fix of test
  test suite for BUG#2809
mysql-test/t/union.test:
  test suite for BUG#2809
sql/mysql_priv.h:
  removed unused parameter of setup_tables()
sql/sql_base.cc:
  removed unused parameter of setup_tables()
  cleanup of unused code
sql/sql_class.h:
  removed unused field
sql/sql_help.cc:
  removed unused parameter of setup_tables()
sql/sql_insert.cc:
  removed unused parameter of setup_tables()
sql/sql_lex.cc:
  excluded duplicate tables finding for UNION
sql/sql_load.cc:
  removed unused parameter of setup_tables()
sql/sql_olap.cc:
  removed unused parameter of setup_tables()
sql/sql_prepare.cc:
  removed unused parameter of setup_tables()
sql/sql_select.cc:
  removed unused parameter of setup_tables()
  revert old BUG#2508 patch
sql/sql_union.cc:
  revert old BUG#2508 patch
  removed unused code
sql/sql_update.cc:
  removed unused parameter of setup_tables()
sql/table.h:
  shared used only for multi-update for now