Avoid getmntinfo

- getmntinfo can take struct statfs or statvfs depending on the
  OS. Use getvfsstat and if not found getfsstat instead. Idea from
  Dan Winship.
- g_local_file_query_filesystem_info(): use statvfs.f_fstypename
  if available

https://bugzilla.gnome.org/show_bug.cgi?id=617949