#492 broken URLs in user guide (X-Face)

[Mike Kupfer]

mh-e.texi in Emacs master has a comment in the section on x-face that says that one or more of the listed URLs no longer works.

@c FIXME: These URLs do not seem to work any more.
Next is the traditional @samp{X-Face:} header field@footnote{The

I'm flagging that here to give the issue more visibility.