Minor doc updates:

 * -bmalware, note that not running as invoking user and emphasize that it's
   for debugging Exim, not for general scanning.
 * permit_codedump ?  coRedump.
 * Anon SSL lacking cert has been confirmed, fix works, remove the
   "(I believe)" (which also might have been inferred to mean I did the
   diagnosis; I didn't, I just convinced myself that Martin's analysis was
   correct).