* Updated to ZDoom 4221:
- Dropped items with the DONTGIB flag set will no longer be destroyed by crushers.
- Fixed: Voxel rendering completely fell apart when a mirror came into view. [Software renderer only. OpenGL was and still is fine.]
- Force all voxel mip levels to use the same pivot point as the first level.
- Added DONTGIB flag to Key, so key-dropping enemies can be used reliably near crushers.
- Fixed: When trying to unmorph a monster, make sure the morphed version doesn't have the TOUCHY flag set, or checking the position of the unmorphed version will kill the morphed version, since they will both exist in the same place at the same time, and TOUCHY is really touchy about that.
- Use tests less prone to overflow on very steep slopes when detecting which side of a plane the camera is on. Mostly, this means testing the distance of the camera to the plane rather than computing the plane's Z at the camera and comparing that with the camera's Z. [Software only, OpenGL was and still is fine.]
- Added CROUCHABLEMORPH flag for the PlayerPawn class. Use this to indicate that a morphed player class can crouch. (Regular players can always crouch, hence the name CROUCHABLEMORPH and not CANMORPH or ALLOWMORPH.)

git-svn-id: http://mancubus.net/svn/hosted/gzdoom/trunk@1552 b0f79afe-0144-0410-b225-9a4edf0717df