mail/mailman: update to 2.1.30 - bug fix (incl. data loss)

• upstream changelog:

https://bazaar.launchpad.net/~mailman-coders/mailman/2.1/view/head:/NEWS#L6

Note that upstream means 2.1.30 to be the final 2.x release,
because it relies on Python 2.x which is EOL upstream.

! MAJOR DATA LOSS FIX, rename all templates/* files to .sample,
! and list them as a @sample in pkg-plist, because they can be edited
! through the web server, and an upgrade should not stomp over edited files.

• rearrange makefile a bit (portlint, portfmt)
• update and upload new htdig patch
• expose NLS port option to pkg-install script to avoid failure
• patch upstream bin/check_perms script to not complain about tightened- up messages/ and mailmanprefix (${PREFIX}/mailman) permissions that we set to 0755 instead of 02775. Mailman should not need to write outside designated directories or create new top-level directories in its install.
• fix a typo in the German (mailman.po) translation
• tweak pkg-install to:
  • leave ${PREFIX}/mailman permissions alone and not set them to 02775
  • fix up non-moved .sample files if pkg-install is run with -I
  • create a copy of mm_cfg.py from mm_cfg.py.dist if missing (-I)
  • create a newsyslog.conf.d/mailman.conf if missing, from examples/mailman.newsyslog.sample if installed (-I)
  • not attempt to fix messages/ (translations) permissions if the NLS port option is disabled
• tweak pkg-plist so that the proper permissions and groups are set by default already
• clean up pkg-message, thanks to bapt@ for pointing out that a missing type: means "install or upgrade".

MFH: 2020Q2 (@samples is an important fix against data loss on update)