Add an entry for the avfilter_draw_slice() API changes implemented in

r20734.

Originally committed as revision 20735 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/APIchanges

@@ -12,6 +12,9 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
+2009-12-05 - r20734 - lavfi 1.12.0 - avfilter_draw_slice()
+  Add a slice_dir parameter to avfilter_draw_slice().
+
 2009-11-26 - r20611 - lavfi 1.11.0 - AVFilter
   Remove the next field from AVFilter, this is not anymore required.