don't load plugins twice.
Not exactly sure where that feature crept in some time ago. It was suppressed by checking to see if a queue plugin was already registered, and then bailing out on subsequent register_hook runs. I noticed it in testing, b/c I didn't have a queue plugin loaded. This removes the duplicate calls to register_hook.
* adds caching of the AUTH methods. You can't add new plugins or register new
hooks w/o restarting QP, so cache the list and avoid having to generate it on every connection.
* other PBP changes (early exits, less indention, fewer unnecessary parens, etc.)
reimplemented dmarc module to use Mail::DMARC
updated SPF plugin to save SPF results in dmarc_spf note
update dkim to store DKIM results in dkim_result & dkim_verifier notes
added max_size on config, so it's likely to get noticed, since even 1M is probably too low for most sites. This should likely default to the same as databytes?
