Remove the X- prefix from some headers

[Barry Warsaw]

MM3 still uses a lot of X- headers, but some of the X- prefixes can be removed. In general, we can just claim the Mailman- prefix for Mailman specific headers. Candidates include:

Mailman-Rule-Hits
Mailman-Rule-Misses
Mailman-Version
Mailman-Approved-At
Mailman-LMTP-MailFrom (i.e. X-MailFrom)
Mailman-Copy (or remove this header)
Mailman-Content-Filter (from X-Content-Filtered-By)

Also, fix the outdated comments about add-dup-header in avoid_duplicates.py and verp.py.

Probably also get rid of X-List-Administrivia (and possibly reduced_list_headers). These seem unnecessary now.

[Barry Warsaw (barry)]

Also, from the mailman-developers thread, possibly:

X-Mailman-Version -> List-Agent
X-Mailman-Approved-At -> List-Approved-Date

[Barry Warsaw (barry)]

See http://www.faqs.org/rfcs/rfc2616.html User-Agent description for possible syntax of List-Agent. There's also currently some debate in the mailing list about whether it should be Mediator, User-Agent, or List-Agent.

[Barry Warsaw (barry)]

See also this draft: http://www.blackops.org/~msk/draft-kucherawy-received-state.txt

[Abhilash Raj (raj-abhilash1)]

This bug has been moved to the new gitlab repo here: https://gitlab.com/mailman/mailman/issues/31

[Junien F (axino)]

Why would X-List-Administrivia be unnecessary now ?