Fix the behaviour that diff(a,b) == -diff(a,b)
Fix the behaviour that diff(a,b) == -diff(a,b)


20070607152823-93b9a-389884ffd15e8e7be47fc0fb9b183b1be0fe14b9.gz

freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut,freedesktop-unofficial-mirror/telepathy__telepathy-salut