Add missing external declaration for kmvc codec

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@5274 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/avcodec.h

@@ -2200,6 +2200,7 @@ extern AVCodec zmbv_decoder;
 extern AVCodec avs_decoder;
 extern AVCodec smacker_decoder;
 extern AVCodec smackaud_decoder;
+extern AVCodec kmvc_decoder;
 
 /* pcm codecs */
 #define PCM_CODEC(id, name) \