Added tests for != predicate.
sql_select.cc:
  Fixing bugs in Item_equal code:
  added a parameter in substitute_for_equal_field;
  modified eliminate_item_equal.
sql_list.h:
  Cleanup


sql/sql_list.h:
  Cleanup
sql/sql_select.cc:
  Fixing bugs in Item_equal code:
  added a parameter in substitute_for_equal_field;
  modified eliminate_item_equal.
mysql-test/t/range.test:
  Added tests for != predicate.