conf/163508: [rc.subr] [patch] Add "enable" and "disable" commands to rc.subr

[Maxim Ignatenko]

> If the 5% of cases are when someone has done something complicated to the rc.conf file, then I don't care: they won't use this interface and we can detect this case and do nothing.

Now I don't see how to distinguish cases when ${rcvar} set to default
value in rc-script and when it's set in other file in some not obvious
way.