I got my changes committed.

It now uses xmlReadIO instead of xmlParseFile, so it should handle 'tricky' AKA non-ASCII/ANSI filenames on Windows.

Additionally, it now has an extension for .svgz and the saving and loading inside of repr-io.cpp handles the compression using zlib ourselves, so it should work nice on Linux *and* on Windows with not tricky futzing.

To do this, I started using the stuff in Inkscape::IO / src/io/*

Take a peek and see if this stuff works for you guys also.