Here are some enhancements to sushi's System Maintenance menu.
To summarize the changes:
* Make a backup of the file before modifying it.
* Fixes to get all menus/forms working.
* Missing/invalid settings (like in rc.conf and inetd.conf)
have been added/removed.
* Most files don't get overwritten now but are edited instead.
So specials settings in e.g. /etc/rc.conf don't get lost now.
* Some help menu fixes. ($NetBSD$ tag has been removed because I
don't see how it would be useful for either user or developer).
