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.


mysql-test/r/grant2.result:
  test result
mysql-test/t/grant2.test:
  test case
sql/sql_parse.cc:
  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.