add multiple inclusion guards to headers

Originally committed as revision 9345 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h263_parser.h

@@ -19,6 +19,11 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+#ifndef AVCODEC_H263_PARSER_H
+#define AVCODEC_H263_PARSER_H
+
 #include "parser.h"
 
 int ff_h263_find_frame_end(ParseContext *pc, const uint8_t *buf, int buf_size);
+
+#endif