gtk.get_current_event_time() will return 0 if there's no "current
event" (which will happen if this is invoked from a SugarKeyGrabber
callback, because that intercepts events below the gtk level). And
libwnck will g_warn if we pass "0" to window.activate(). Since
matchbox doesn't look at the timestamp anyway, it's simplest to just
always pass "1" there.
(Needed for part of #2159)
56d8e5e748