Predictable message-ids

Outbound message-ids are predictable, with a consistent code unique and
static to each osTicket installation. This will help detect email loops
where message is delivered back to the system in an email loop.
Log errors on email loop detection

If an email loop is detected, in addition to dropping the message, also log
an error to the system log, but do not send an email to the administrator in
the event that it is the administrator's email that is looped.