try to support multiple mice, fail

it seems the event.deviceid parameter is not passed through events in pygtk

according to the GTK C API, it is present:

http://www.gtk.org/tutorial1.2/gtk_tut-29.html

this is also the case in this tutorial:

http://www.pygtk.org/pygtktutorial/sec-addingxinputsupport.html

... which doesn't compile here. it is *not* present in our event so we have no way of uniquely identifying pointers (name is the same, even memory hashes are the same)

see #4516