Fixed a regression in Qsmtp.messageObject.  from_address_desc is now optional.

If from_address_desc is null or empty string, from_address will
be used instead.

This was causing Ganymede to fail to send email at shutdown if
the recently added ganymede.returnaddrdesc property was not set.
Fixed a bug that could prevent the internal mail queue from draining

The DBLog.close() method was only waiting for the mailer to drain if
and only if the DBLog was logging mailout events to disk.

This is obviously incorrect, we always need to wait for the mailer to
drain before terminating.