#338 publish can be very slow...

[Arno Waschk]

publish can be incredibly slowed down by one single slow
(or throttled or busy or whatever) block server, since we
always wait for the response or timeout of it before
continuing.
Brokers which are sometimes slow and sometimes not can
get a high sigma (like 1000), which is for some reason
made to produce horribly long timeouts due to sigma
multiplication. [;)]
So we might want a mechanism to bypass that.
A single slow broker could get SPOF privs otherwise.