[RFH] leading dots in manpages

The git-shortlog manpage has a "files" section that mentions ".mailmap".
Asciidoc correctly renders this in the HTML version, but in the manpage,
the line that should say ".mailmap" is omitted. This seems to be caused
by the line

.mailmap::

being misinterpreted somewhere (though the .xml file looks reasonable).

It looks like the same problem as 7c8b5eaf, but we just dodged the
problem there. Is there an actual fix?

-Peff