instance pointer from EmissionHook?

[Richard Hestilow <hestilow ximian com>]

I'm porting gnome sound events to gtk+2, and noticed that in an
EmissionHook callback there doesn't seem to be any way to get a
reference to the actual object that emitted the signal. Looking at
gobject sources indicates that the pointer is known, just isn't
accessible. Any ideas? This is pretty necessary for sound events,
because there are some per-object things that need to be checked before
playing anything.

-- Richard