Ticket #3052: fix man page "macro `\' not defined" warnings.
man --warnings doc/man/mc.1 >/dev/null
reported the following warning:
3114: warning: macro `\' not defined".
and indeed man page didn't look correct at the line starting with "Apply
escaping".
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>