A first pass in attempts to fix crashes when ACS causes map changes.
Frustratingly still got a crash, but I think this is definitely the right foundation to work with.
- There's a freeze cheat bool to freeze everything except for players.
- There's a level freeze bool to freeze literally everything.
- There's a frozen bool on mobj_t to explicitly control freeze status on an object.
- Sprite tilts back and forth 5.625 degrees, two tics each
side, for 17 tics (half a second).
- Turning is ignored--as if in the air--every other tic
during those 17 tics.
