Quick and dirty fix to allow WriteXmlIfChanged to write xml in utf-8, co...

This is a quick and dirty fix to allow node-gyp to generate the vcxproj when the are latin-1 characters in the paths.

I'm no pyton guy, and I just solved my problem with latin-1 characters. There is still the need to only convert when needed, but I don't know how to do that.. Maybe there other encodings that should be tested.

WriteXmlIfChanged was not actually writing in utf-8, but in ascii. Converting directly to utf-8 would fail if unicode(string, native_enconding) is not called first.