Similar to previous removals of g_cclosure_marshal_VOID__VOID we can remove
other marshallers for which are a simple G_TYPE_NONE with single parameter.
In those cases, GLib will setup both a c_marshaller and va_marshaller for
us. Before this commit, we would not get a va_marshaller because the
c_marshaller is set.
Related to GNOME/Initiatives#10
Tools on the same physical item have the same serial number, so the eraser
and the pen part of a single pen share that serial number. With the current
lookup code, we'll always return whichever tool comes first into proximity.
Change the code to use the hw id in addition to the serial number, this way we
can differ between two tools.
