Added new logic to ACL system:

1) If GRANT OPTION (not mysql db):
   Ok to update existing user, but not password.
   Not allowed to make a new user.

2) If UPDATE_ACL to mysql DB:
   Ok to update current user, but not make a new one.

3) If INSERT_ACL to mysql DB:
   Ok to add a new user, but not modify existing.

4) If GRANT OPTION to mysql DB:
   All modifications OK.