Extending the man page search path

When you add packages, sometimes their man pages are not properly added to the $MANPATH used to find them using the man path.

If $MANPATH is prefixed by a : then its value will be added to the default path. So the issue here is that when $MANPATH is null, no leading colon is used, which it why the man_db config is being ignored. So replacing

 MANPATH="${MANPATH:+$MANPATH:}/opt/symas/share/man"

by a simpler

 MANPATH="${MANPATH-}:/opt/symas/share/man"

would be enough to solve the issue.