ClutterTimeline: Fix the 'msecs' parameter for the new-frame signal

Between Clutter 0.8 and 1.0, the new-frame signal of ClutterTimeline
changed the second parameter to be an elapsed time in milliseconds
rather than the frame number. However a few places in clutter were
still calling the parameter 'frame_num' which is a bit
misleading. Notably the signature for the signal class closure in the
header was using the wrong name. This changes them to use 'msecs'.

tests/conform/test-timeline-rewind.c

@@ -35,11 +35,9 @@ watchdog_timeout (TestState *state)
 
 static void
 new_frame_cb (ClutterTimeline *timeline,
-              gint frame_num,
+              gint elapsed_time,
               TestState *state)
 {
-  gint elapsed_time = clutter_timeline_get_elapsed_time (timeline);
-
   if (elapsed_time == TEST_TIMELINE_DURATION)
     {
       g_test_message ("new-frame signal received (end of timeline)");