Fix rc.d scripts manual startup behavior

Should fix the behavior of the rc.d scripts to be consistent with common sense usage, e.g. manually running "[/usr/local]/etc/rc.d/<service> start" will start the service no matter whether it has an "<service>_enable" in /etc/rc.conf[.local].

The rc.subr library should be modified to interpret the "<service>_enable" statements in rc.conf as a tip to whether start it on boot or not, and not to limit manual usage of the service.