Log Message:
Do not use deprecated GnuTLS functions
http://bugzilla.gnome.org/show_bug.cgi?id=648606
require minimally gnutls 2.2.0 for use of currently used functions

since the recent gnutls update, deprecated => obsoleted
fixes build for now, discussing with wiz@ seems reasonable later
to update to the gnome3 version and, if necessary, adding back vino2.