Otherwise doxygen complains about ambiguous filenames when files exist
under the same name in different subdirectories.

Originally committed as revision 16912 to svn://svn.ffmpeg.org/ffmpeg/trunk

Originally committed as revision 15673 to svn://svn.ffmpeg.org/ffmpeg/trunk

submitted by Anuradha Suraparaju, anuradha rd.bbc.co uk

Originally committed as revision 13041 to svn://svn.ffmpeg.org/ffmpeg/trunk