Add an entry for the AVFilter.next field removal.

Originally committed as revision 20614 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/APIchanges

@@ -12,6 +12,9 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
+2009-11-26 - r20611 - lavfi 1.11.0 - AVFilter
+  Remove the next field from AVFilter, this is not anymore required.
+
 2009-11-25 - r20607 - lavfi 1.10.0 - avfilter_next()
   Introduce the avfilter_next() function.