Disallow the combination VACUUM FULL FREEZE for safety's sake, for the

Disallow the combination VACUUM FULL FREEZE for safety's sake, for the
reasons I outlined in pghackers a few days ago.

Also, undo someone's overly optimistic decision to reduce tuple state
checks from if (...) elog() to Asserts.  If I trusted this code more,
I might think it was a good idea to disable these checks in production
installations.  But I don't.