APIchanges: mention cleaned up header includes

Fixes bug 188.
Signed-off-by: NJonathan Nieder <jrnieder@gmail.com>
Signed-off-by: NJanne Grunau <janne-libav@jannau.net>

doc/APIchanges

@@ -124,8 +124,10 @@ API changes, most recent first:
 2011-09-03 - c11fb82 - lavu 51.10.0
   Add AV_OPT_SEARCH_FAKE_OBJ flag for av_opt_find() function.
 
-2011-08-26 - f2011ed - lavu 51.9.0
-  Add av_fifo_peek2(), deprecate av_fifo_peek().
+2011-08-26 - lavu 51.9.0
+  - f2011ed Add av_fifo_peek2(), deprecate av_fifo_peek().
+  - add41de..abc78a5 Do not include intfloat_readwrite.h,
+    mathematics.h, rational.h, pixfmt.h, or log.h from avutil.h.
 
 2011-08-16 - 48f9e45 - lavf 53.4.0
   Add avformat_query_codec().