Configure: produce useful dependency errors
Configure: produce useful dependency errors

I discovered that PKG_CHECK_MODULES sets a variable if the dependencies
aren't found containing the message it would have died with if you
hadn't specified ACTION-IF-NOT-FOUND. So this gives us better output,
without breaking opportunistically adding Call (etc.) support (as I
did).

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