Switch-case made less buggy, now with PATCH!

[Chad J]

http://d.puremagic.com/issues/show_bug.cgi?id=3536

So Walter, with this you can keep your beloved fall-through.
Now can the rest of us be spared the nasty fall-through bugs, please
please please??

Also, about assert(0)... I'd be happy to change what I did if Walter and
associates feel that adding assert(0) to the list is worth its minor
complications.

(Sorry I don't have a patch for properties, but that one's harder.)

- Chad