Bug 621213 – GDBusProxy and well-known names

Allow constructing a GDBusProxy for well-known names as discussed here
http://mail.gnome.org/archives/gtk-devel-list/2009-October/msg00075.html
including test cases.

Make it possible to create a GDBusProxy for a GBusType instead of a
GDBusConnection. This requires G_BUS_TYPE_NONE so add that too.

Nuke g_bus_watch_proxy() since one can now more or less use GDBusProxy
for this.

Port gdbus-example-watch-proxy to this new API and include this
example in the GDBusProxy doc page.

Also nuke the GType parameter from the GDBusProxy constructors as
requested here: https://bugzilla.gnome.org/show_bug.cgi?id=621229

Also update the porting guide and other API docs for this change.

Also fix a bug in the signal dispatching code so each subscriber only
get notified once, not N times, for the same signal. Also add a test
case for this.

https://bugzilla.gnome.org/show_bug.cgi?id=621213



Signed-off-by: David Zeuthen <davidz@redhat.com>