Add APIchanges entry after r24728.

Originally committed as revision 24729 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/APIchanges

@@ -13,6 +13,9 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
+2010-08-07 - r24728 - lavfi 1.28.0 - AVFilterBuffer
+  Move format field from AVFilterBuffer to AVFilterPicRef.
+
 2010-08-06 - r24709 - lavcore 0.3.0 - av_check_image_size()
   Deprecate avcodec_check_dimensions() in favor of the function
   av_check_image_size() defined in libavcore/imgutils.h.