This reverts commit 0283906a and also
fixes the bug, all in one!

The original commit was not correct: it conflated UNIX time
(g_get_real_time) with X11 time (gtk_get_current_event_time). The
easiest way to fix it would be to simply call the later instead of the
former, but I also want to revert to using the more explicit API where
the caller must pass the user time manually, so do that too.