Bugfix: fix mail forwarding

 * we can't make the mailer run on background, since the next thing we do is to
   remove the input file used to feed the mailer. Depending on which process
   runs first, you end with "sometimes not getting the mail forwards" or even
   no forwarded mails at all. In the future this code should be refactored so
   we stop blocking here -- but let's do it the safe way.
 * recent mailx versions are more string about input and input order. We cannot
   have newlines on subjects, and the subject parameter must come before the
   recepient argument.