Update the task backend to provide a mechanism for sending e-mail messages to
notify administrators whenever a given task has been completed.  It is possible
to specify a set of administrators that should be notified only if the task
does not complete successfully, and/or a set of administrators that should be
notified regardless of the task's success or failure.  The basic framework for
this capability has always been in place, and this change only provides the
final implementation that actually generates and sends the e-mail message.

This also includes a change to the way that log messages are handled so that
any messages logged by a thread executing a task (or any DirectoryThread
subclass created by a task thread) will be captured as part of that task.
These messages will also be included in the notification e-mail message.

OpenDS Issue Numbers:  2033, 2034