SPF HELO, and weirdly related enhancements 

* move is_ipv4_literal from plugins/helo.checks to net_utils, so it's available for the SPF plugin

* SPF: skip HELO tests for IP literals

* SPF: when a connection has relaying permissions, use our (Haraka's) public IP in the SPF mail_from query, to determine if Haraka has permisison to send on behalf of that MAIL FROM domain.

* move the public_ip setting out of config/connect.geoip.ini to config/smtp.ini, used by GeoIP and SPF plugins.

* updated connect.geoip to use boolean config options