Log Message:
Update to 20181128. Changes:

- Add qmail-qfilter-queue, which is like qmail-qfilter-ofmipd-queue
  and qmail-qfilter-smtpd-queue but requires an environment variable
  pointing to a config file (QMAILQUEUEFILTERS) rather than
  hardcoding one.
- Leave qmail-qfilter-ofmipd-queue and qmail-qfilter-smtpd-queue as
  thin wrappers around qmail-qfilter-queue, logging what the sysadmin
  needs to do.