Man page fix to make mutt.man translatable

The manpages-l10n project maintains the translation of mutt(1) for a while, but for some of the last versions, po4a is unable to create a translation template:

../upstream/archlinux/man1/mutt.1:107: (po4a::man)
Unsupported font in: '\fC\&    mutt \-a image.jpg \-\- to-addr
\&    mutt \-a img.jpg *.png \-\- to-addr-1 to-addr-2
'.

So we are unable to keep the translations up-to-date. See the attached file, which fixes the problem.manpage.diff