Comment 3 for bug 612111

I just noticed that VM also used this code to display MIME encapsulated forwarded messages, this resulted in an infinite loop of forwarded message buttons since the headers were included and had the forwarded message content description. I offer this patch to handle the issue, but it may need to be looked into some more. In fact, I'm not even sure the headers need to be inserted for the vm-mime-types-match = "message", but rather only for vm-mime-types-match "multipart/digest"