property_changed_cb now only passed as a callback once, fix signature & warnings
property_changed_cb now only passed as a callback once, fix signature & warnings

freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control