include all prerequisites in header files

Originally committed as revision 9344 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/dv.h

@@ -25,6 +25,8 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#include "avformat.h"
+
 typedef struct DVDemuxContext DVDemuxContext;
 DVDemuxContext* dv_init_demux(AVFormatContext* s);
 int dv_get_packet(DVDemuxContext*, AVPacket *);