Add an entry for the avfilter_next() function addition.

Originally committed as revision 20608 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/APIchanges

@@ -12,6 +12,9 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
+2009-11-25 - r20607 - lavfi 1.10.0 - avfilter_next()
+  Introduce the avfilter_next() function.
+
 2009-11-25 - r20605 - lavfi 1.9.0 - avfilter_register()
   Change the signature of avfilter_register() to make it return an
   int. This is required since now the registration operation may fail.