#37 Adjust zone controller logic upon damper failure discovery

[Vadim Tkachenko]

(depends on bug #864816)

Currently, the damper failure is ignored. In the
future, it may be a good idea to a) report the failure
b) modify the demand calculation and damper balancing
routine in such a way that the damper for the zone is
excluded.

Issue to consider: suppose the damper has failed when
[slmost completely] closed. In this case, boom, we're
screwed, and must ignore the zone altogether, because
it wouldn't be possible to satisfy it, period. However,
if the throttle was more than a certain threshold, it
would still be possible to satisfy that zone, and its
demand should be taken into account.