Use full path for #includes from another directory.

Originally committed as revision 13098 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/file.c

@@ -18,8 +18,9 @@
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
+
+#include "libavutil/avstring.h"
 #include "avformat.h"
-#include "avstring.h"
 #include <fcntl.h>
 #include <unistd.h>
 #include <sys/time.h>