Starting to add infrastructure for getting and setting event
priorities in threadsafe manner.
Fixed one source of deadlock: if an event goes into its first phase of
commit, it holds a lock on the entire event.  If a network exception
then arose, waldoActiveEventMap would then try to set the network
failure condition on the entire event.  This could lead to deadlock
because setting the network failure condition was protected by the
same lock that the entire event was already holding (for committing).
Ended up just protecting network failure condition with a separate lock.