create user 'someuser'@'%' identified by 'password';
grant all privileges on somedb.* to 'someuser' with grant option;

$ mysql -u someuser -p
> Enter Password:
> ERROR 1045 (28000): Access denied for user 'someuser'@'localhost' (using password: YES)

mysql> SELECT * FROM user WHERE user='' AND host='localhost';

mysql> DELETE FROM user WHERE user='' AND host='localhost';

FLUSH PRIVILEGES;