If we're to support sysvinit and systemd at the same time, let each use
their upstream paths. This means sysvinit gets /sbin/init.

This also means that business can continue as usual, and nobody is forced
to install eselect-init. The current system works for users who don't care
or aren't aware of this innovation. Motivated users who want the ability to
change back and forth can emerge eselect-init and modify their init= line
in the bootloader.

This is cleaner because it keeps things more in lockstep with upstream.

This is also politically easier, as it doesn't require any notable changes
or new ebulds to openrc folks, which I can imagine might be met with
opposition here and there.