add message saying that pgmyuv format is deprecated

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@8336 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

ffmpeg.c

@@ -2027,6 +2027,7 @@ static void opt_format(const char *arg)
         pgmyuv_compatibility_hack=1;
 //        opt_image_format(arg);
         arg = "image2";
+        fprintf(stderr, "pgmyuv format is deprecated, use image2\n");
     }
 
     file_iformat = av_find_input_format(arg);