Update APIchanges after r25236.

Originally committed as revision 25238 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/APIchanges

@@ -13,6 +13,10 @@ libavutil:   2009-03-08
 
 API changes, most recent first:
 
+2010-09-27 - r25236 - lavu 50.31.0 - av_set_options_string()
+  Move av_set_options_string() from libavfilter/parseutils.h to
+  libavutil/opt.h.
+
 2010-09-27 - r25227 - lavfi 1.47.0 - AVFilterLink
   Make the AVFilterLink fields srcpad and dstpad store the pointers to
   the source and destination pads, rather than their indexes.