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
given a resource path so that it can be smart about loading from files versus
streams depending on what works based based on where the resources are coming
from. Also moved FastImageIO into com.threerings.resource to avoid a dependence
on com.threerings.media in resource.
git-svn-id: svn+ssh://src.earth.threerings.net/nenya/trunk@310 ed5b42cb-e716-0410-a449-f6a68f950b19