Fixed Transient reader locking broken by 4310f8b (#161)

Fixed Transient reader locking broken by 4310f8b (#161)

The closeForWriting() call comment is correct -- we must keep the lock,
but the optional argument was accidentally lost (when undoing the failed
attempt to remove all long-term transient locks in the feature branch).

Also polished stale comments (which led to the above bug discovery!).

Also polished addEntry() aspects that I have missed in 4310f8b.