Ensure all group flags are printed in mixin's debug output
Ensure all group flags are printed in mixin's debug output

The stringification code has a case for the first eight members of the
TpChannelGroupFlags enum, but didn't do anything with any unhandled
flags.

Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib,Distrotech/telepathy-glib