Bugfix #21051: Restored 'Playback FPS'

This commit restores the 'Playback FPS' option which showed an indicator of the frame rate of animation playback in the 3D-View.

The info for this is now stored in a temp struct in scene data, with the status info being updated by the "animation step" operator instead of relying on globals as the old code did. This seems a lot more stable than in 2.49, but the accuracy is still questionable.

source/blender/editors/include/ED_screen.h

@@ -107,7 +107,9 @@ void	ED_screen_new_window(struct bContext *C, struct rcti *position, int type);
 
 /* anim */
 void	ED_update_for_newframe(const struct bContext *C, int mute);
+void 	ED_refresh_viewport_fps(struct bContext *C);
 
+/* screen keymaps */
 void	ED_operatortypes_screen(void);
 void	ED_keymap_screen(struct wmKeyConfig *keyconf);