client-factory: prepare TP_CHANNEL_FEATURE_CONTACTS
client-factory: prepare TP_CHANNEL_FEATURE_CONTACTS

We are about to use the channel-contacts API so best to make sure they will
work.

https://bugzilla.gnome.org/show_bug.cgi?id=675229

GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets