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'.

clutter/clutter-alpha.c

@@ -149,7 +149,7 @@ static GParamSpec *obj_props[PROP_LAST];
 
 static void
 timeline_new_frame_cb (ClutterTimeline *timeline,
-                       guint            current_frame_num,
+                       guint            msecs,
                        ClutterAlpha    *alpha)
 {
   ClutterAlphaPrivate *priv = alpha->priv;