* Recent collision update caused a regression where the player would get
"stuck" while standing on top of a solid doodad, unable to walk left
or right.
* When deciding if the actor is on top of a doodad, use the doodad's
Hitbox (if available) instead of the bounding box. This fixes the
upside-down trapdoor acting solid when landed on from the top, since
its Hitbox Y coordinate is not the same as the top of its sprite.
* Cheats: when using the noclip cheat in Play Mode, you can hold down
the Shift key while moving to only move one pixel at a time.