Enhance the rc.d framework for better manageability

The current rc.d framework is hard to automatically manage and requires a big amount of manual tweaking. It's also worth trying to optimize it (e.g. run services in parallel/background).

Ideas:
 * create an /etc/init.d -> /etc/rc.d symlink to ease the pain of transitioning users from other *nix plaforms
 * get a "service" tool/script to ease rc.d scripts actions, wherever they are placed
 * perhaps make rc.d scripts be able to reconfigure themselves and change /etc/rc.conf[.local]
 * see whether other startup frameworks can be adapted (Upstart, launchd, Puppet)

References:
 * http://docs.freebsd.org/cgi/mid.cgi?b58b3fc7f4a07c9b6d55741e2ec25f47.squirrel
 * http://www.freebsd.org/cgi/query-pr.cgi?pr=138460