Call mpegvideo flush routine on h264 flush. Needed in particular

to clear last_picture_ptr, next_picture_ptr for proper picture
management. Prevents crashes in error concealer following seeks.
Fixes Roundup issue 189.

Originally committed as revision 11049 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264.c

@@ -3342,6 +3342,7 @@ static void flush_dpb(AVCodecContext *avctx){
     if(h->s.current_picture_ptr)
         h->s.current_picture_ptr->reference= 0;
     h->s.first_field= 0;
+    ff_mpeg_flush(avctx);
 }
 
 /**