In case of database level grant the database name may be a pattern,
in case of table|column level grant the database name can not be a pattern.
We use 'dont_check_global_grants' as a flag to determine
if it's database level grant command 
(see SQLCOM_GRANT case, mysql_execute_command() function) and
set db_is_pattern according to 'dont_check_global_grants' value.