Add a changelog entry for the RTSP tunneling, that was added a few weeks ago

Originally committed as revision 23899 to svn://svn.ffmpeg.org/ffmpeg/trunk

Changelog

@@ -15,6 +15,7 @@ version <next>:
 - libfaad2 wrapper removed
 - DTS-ES extension (XCh) decoding support
 - native VP8 decoder
+- RTSP tunneling over HTTP