s/cvs/svn for ffmpeg

configure.ac

@@ -2722,7 +2722,7 @@ dnl Trying with pkg-config
         if test "${enable_sout}" != "no"; then
             VLC_ADD_BUILTINS([stream_out_switcher])
         fi],
-         [ AC_MSG_ERROR([Could not find ffmpeg on your system: you may get it from http://ffmpeg.sf.net/ (cvs version is recommended). Alternatively you can use --disable-ffmpeg to disable the ffmpeg plugins.]) ], [$LDAVUTIL])
+         [ AC_MSG_ERROR([Could not find ffmpeg on your system: you may get it from http://ffmpeg.sf.net/ (svn version is recommended). Alternatively you can use --disable-ffmpeg to disable the ffmpeg plugins.]) ], [$LDAVUTIL])
 
       
       AC_CHECK_LIB(avformat, av_open_input_stream, [