trying to enable a view with no expressions (or no tables) should trigger a better error message

[greenlion]

mysql> call flexviews.create_mvlog('test','bozo');
Query OK, 1 row affected (0.01 sec)

mysql> call flexviews.create('test','mv2','INCREMENTAL');
Query OK, 0 rows affected (0.00 sec)

mysql> call flexviews.add_table(1, 'test','bozo', 'bzo', null);
Query OK, 1 row affected (0.01 sec)

mysql> call flexviews.enable(1);
ERROR 1644 (45000): COULD NOT VALIDATE MATERIALIZED VIEW. CHECK @MV_DEBUG.