StatefulDBusProxy: make calling invalidate() twice not be an error
StatefulDBusProxy: make calling invalidate() twice not be an error

We should just ignore the second invalidate() call and keep the first
one, with a debug message.

Also, add debug messages. When debugging we will probably want to know
when a service dies.

anantkamath/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt4,TelepathyIM/telepathy-qt,special/telepathy-qt-upstream,tiagosh/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt4,TelepathyQt/telepathy-qt,detrout/telepathy-qt,anantkamath/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt4,tiagosh/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt,anantkamath/telepathy-qt,tiagosh/telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt4,freedesktop-unofficial-mirror/telepathy__telepathy-qt,freedesktop-unofficial-mirror/telepathy__telepathy-qt,TelepathyQt/telepathy-qt,special/telepathy-qt-upstream,TelepathyIM/telepathy-qt,TelepathyIM/telepathy-qt,TelepathyIM/telepathy-qt,TelepathyIM/telepathy-qt,TelepathyQt/telepathy-qt,special/telepathy-qt-upstream,TelepathyQt/telepathy-qt,tiagosh/telepathy-qt,detrout/telepathy-qt,detrout/telepathy-qt