[Reviewer Matt] Add deadlock detection to eventq

Matt

Can you review the cpp-common changes adding deadlock detection to the eventq.  I'll send a subsequent pull request for the Sprout changes once this is pulled to the master branch.

There's also a minor change to the load monitor to fix a NaN sometimes displayed in logs.

Mike
This feels a bit unpleasant.  The method is called `deadlock_check` but it actually updates `_service_time`.