Improve behavior of log_lock_waits patch. Ensure that something gets logged

even if the "deadlock detected" ERROR message is suppressed by an exception
catcher.  Be clearer about the event sequence when a soft deadlock is fixed:
the fixing process might or might not still have to wait, so log that
separately.  Fix race condition when someone releases us from the lock partway
through printing all this junk --- we'd not get confused about our state, but
the log message sequence could have been misleading, ie, a "still waiting"
message with no subsequent "acquired" message.  Greg Stark and Tom Lane.