framemd5_class and md5enc_class may not be identical.

Due the crappy issue of classes having to be unique,
we cannot even have classes with identical content,
otherwise the compiler or linker is free to merge them,
giving the same result and bugs as if we had only one class.
Besides redesigning the option code to handle this correctly
I see only the option of requiring any two classes to have
different names, but the list of requirements for
AVClasses is getting kind of unmanageable.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavformat/md5enc.c

@@ -141,7 +141,7 @@ static int framemd5_write_trailer(struct AVFormatContext *s)
 }
 
 static const AVClass framemd5_class = {
-    .class_name = "hash encoder class",
+    .class_name = "frame hash encoder class",
     .item_name  = av_default_item_name,
     .option     = hash_options,
     .version    = LIBAVUTIL_VERSION_INT,