relay plugins

https://github.com/smtpd/qpsmtpd/pull/13


replaces 3 relay plugins (check_relay, check_norelay, relay_only) with a single plugin (relay).

Same functionality. 
Bonus: includes tests. And a brief description of how the settings in the 3 config files interact. :)


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  Matt Simerson                   http://matt.simerson.net/
  Systems Engineer            http://www.tnpi.net/

  Mail::Toaster  - http://mail-toaster.org/
  NicTool          - http://www.nictool.com/
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