Clarify --help output about Vorbis and Theora.

Originally committed as revision 7769 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -89,8 +89,8 @@ show_help(){
   echo "  --enable-mp3lame         enable MP3 encoding via libmp3lame [default=no]"
   echo "  --enable-libnut          enable NUT support via libnut [default=no]"
   echo "  --enable-libogg          enable Ogg support via libogg [default=no]"
-  echo "  --enable-libtheora       enable Theora support via libtheora [default=no]"
-  echo "  --enable-vorbis          enable Vorbis support via libvorbis [default=no]"
+  echo "  --enable-libtheora       enable Theora encoding via libtheora [default=no]"
+  echo "  --enable-vorbis          enable Vorbis en/decoding via libvorbis [default=no]"
   echo "  --enable-x264            enable H.264 encoding via x264 [default=no]"
   echo "  --enable-xvid            enable Xvid encoding via xvidcore [default=no]"
   echo "  --enable-amr_nb          enable amr_nb float audio codec"