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
Will be activated after a little more reviewing and fixing by me.
Commited now, so as to not lose history of that.
Originally committed as revision 16323 to svn://svn.ffmpeg.org/ffmpeg/trunk