clientError and serverError exit after they're done so no need for
break or return. Also, $this->format is default.
We also got rid of the incredibly verbose version of $this->isPost()
which was spread all over the place.
Not all of this cleaning up is done yet.
self-subscription) via the API. Additionally, make it impossible
to block yourself or unsubscribe from yourself, period.
I also made User use the subs.php helper function for unsubscribing
during a block.
Hopefully, these changes will get rid of the problem of people
accidentally deleting their self-subscriptions once and for all
(knock on wood).
