core: also enforce ratelimiter if we stop a unit due to BindsTo=

This extends on bea355da, and extends
the ratelimiter to not only be used for StopWhenUnneeded=1 units but
also for units that have BindsTo= on a unit that is dead.

http://lists.freedesktop.org/archives/systemd-devel/2015-April/030224.html