Improve logging around task disconnect and ensuring we return MACHLOST code...

Improve logging around task disconnect and ensuring we return MACHLOST code rather then TASKDISK when we have lost the machine

	Improve logging around disconnection and machine lost messages as
	part of trying to work out an AAO CCD system failure where unexplained
 	disconnections occur.   Basic approach is that if we have a logging
        routine, we log even if the relevant DITS_LOG_BASIC etc. flags are not
	set.  These are rare events so won't dramatically increase the log size.

	Note - now return DITS__MACHLOST status in cases where we used to
	     return DITS__TASKDISC (which was a mistake).