man: support special characters in filenames

man.sh needs to handle double quotes and sub shell character
as '`' '$' etc.

PR: 275967
Reviewed by: bapt

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D43453

(cherry picked from commit b8a484ec343d163a40f7cf4a6026e880f992c738)