-Merge from trunk into rend32

git-svn-id: http://odamex.net/svn/root/branches/rend32@3917 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Revert r3909. Clipping ceilings and floors to the height of walls even if there are missing upper/lower textures breaks the shadowcasting map trick. Thanks RjY and Ant P.

git-svn-id: http://odamex.net/svn/root/branches/rend32@3921 b0bcef46-2027-0410-bd56-ab726e9a1d04