man/*.man: Replace \(ru with an underscore, e.g. .mh_profile.

man/*.man: Replace \(ru with an underscore, e.g. .mh_profile.

The character is an underscore, and that's what's wanted.
\(ru gives a "rule", which draws as a thick baseline in PDFs;
not a character at all.
Other devices map \(ru onto underscore, e.g. ASCII,
but an underscore should be used in the first place.