mysql-test/r/negation_elimination.result:
  new tests of negation elimination
mysql-test/t/negation_elimination.test:
  new tests of negation elimination
sql/item.h:
  test of boolean functions added
sql/item_cmpfunc.cc:
  NOT subtree is already checked, so wee need to return just argument
sql/item_cmpfunc.h:
  test of boolean functions added
sql/mysql_priv.h:
  'place' to detect WHERE clause
sql/sql_parse.cc:
  function for creation negated expression
sql/sql_select.cc:
  removed unused function
sql/sql_select.h:
  removed unused function
sql/sql_yacc.yy:
  'place' to detect WHERE clause