If we have DELETE with always true WHERE clause we should not use 
optimized delete_all_rows() method for tables with DELETE triggers,
because in this case we will lose side-effect of deletion.


mysql-test/r/trigger.result:
  Added test for bug #5890 "Triggers fail for DELETE without WHERE".
mysql-test/t/trigger.test:
  Added test for bug #5890 "Triggers fail for DELETE without WHERE".
sql/sql_delete.cc:
  mysql_delete(): 
    We should not use optimized delete_all_rows() method for tables
    with DELETE triggers, because in this case we will lose side-effect
    of deletion.
sql/sql_trigger.h:
  Added new Table_triggers_list::has_delete_triggers() method which
  allows to understand quickly if we have some DELETE triggers in
  our list.