fix some win32 problems when OSFS points to root of a drive
fix some win32 problems when OSFS points to root of a drive

Basically, long-format file names the point to a drive are invalid unless they
end with a backslash.  So "\\\\?\\C:" is wrong (and you'll be told it doesn't
exist) while "\\\\?\\C:\\" is right.

zopyx/pyfilesystem,flying-circus/pyfilesystem,piranna/pyfilesystem,pombreda/pyfilesystem,PyFilesystem/pyfilesystem,pmitros/pyfs,rivenz/pyfilesystem,pmitros/pyfs,Konubinix/pyfilesystem