mail/py-spf-engine: Miscellaneous bug fixes and improvements

• Fix runtime error of pyspf-milter that happens when either 'UMask' or 'IntHosts' is set in configuration file.
• Stop installing backup files.
• Make miscellaneous paths consistent between library files, man pages, pkg-message and rc.d script.
• Remove CONFLICTS as mail/postfix-policyd-spf-python is removed from ports tree

MFH: 2022Q3
(cherry picked from commit 00b787288fc81a2e5dba2a62a2627da760772b50)