use boost::filesystem in our own CFileSystem to finally solve mingw filesystem problems
problems were:
* there's no know way to me to compare if 2 paths point to the same directory
* windows versions of POSIX funcs are only half implemented and fail or return bogus
* windows allows a lot complicated filepaths (//MY_SMB/foo, file://c:/adada.txt, ...) saying they wouldn't exist is very critical cause code could try to recreate such files/folders and then overwrite the existing ones
didn't solved the last item yet (don't want to delay 95.0 release), to do that ::IsAbsolutePath() and some other funcs need to switch to boost