Count timeline frames using the FPS instead of an integer interval

Bug 1495 - Timelines run 4% short

Previously the timelines were timed by calculating the interval
between each frame stored as an integer number of milliseconds so some
precision is lost. For example, requesting 60 frames per second gets
converted to 16 ms per frame which is actually 62.5 frames per
second. This makes the timeline shorter by 4%.

This patch merges the common code for timing from the timeout pools
and frame sources into an internal clutter-timeout-interval file. This
stores the interval directly as the FPS and counts the number of
frames that have been reached instead of the elapsed time.

clutter/clutter-frame-source.h

@@ -32,12 +32,12 @@
 
 G_BEGIN_DECLS
 
-guint clutter_frame_source_add (guint          interval,
+guint clutter_frame_source_add (guint          fps,
 				GSourceFunc    func,
 				gpointer       data);
 
 guint clutter_frame_source_add_full (gint           priority,
-				     guint          interval,
+				     guint          fps,
 				     GSourceFunc    func,
 				     gpointer       data,
 				     GDestroyNotify notify);