similar to the recent Zlib addition. This is required for the
RomListWidget, which currently doesn't parse valid PNG files
that are generated outside Stella (in particular, those that
have been optimized and use row filtering).
git-svn-id: svn://svn.code.sf.net/p/stella/code/trunk@2044 8b62c5a3-ac7e-4cc8-8f21-d9a121418aba
stephena