[sugar] Deprecated methods in Tubes API are about to go away

[Simon McVittie]

This change has been committed. One thing I forgot to mention is that
Gabble now echoes broadcast messages (usually meaning signals) back to the
sender as well as delivering them to the other participants, and at some
point Salut will have get same change; this makes Tubes behave more like the
real dbus-daemon. If you're doing something cunning with signals in an
activity, please make sure this won't break it.

	Simon