-Set initial sizes for the HashTables used by TextureManager to reduce the number of HashTable resizes during startup.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4317 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Add TextureManager::freeTexture to release the memory used by a texture and free its handle if one was allocated for it.

git-svn-id: http://odamex.net/svn/root/branches/texmanager@4318 b0bcef46-2027-0410-bd56-ab726e9a1d04