9733142d35
not actually write out new image to a file if we don't need to. This cuts my tileset building from 42 seconds to 22 when no files have changed (as opposed to 4 when it was skipping it altogether, but winding up with a hosed tsbundles.dat), so it's at least a decent bit better. git-svn-id: svn+ssh://src.earth.threerings.net/nenya/trunk@391 ed5b42cb-e716-0410-a449-f6a68f950b19