rewrote how texture chains are handled, they are now stored outside the surfaces...

rewrote how texture chains are handled, they are now stored outside the surfaces, and are rebuilt as the player moves through the world (bmodel texture chains are just left untouched)
good efficiency improvement I think

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@2629 d7cf8633-e32d-0410-b094-e92efae38249