mail_format_ explicitly chooses 2-digit years when formatting network mail

[Eric Swenson]

The subroutine mail_format_ has special case code for formatting dates in email headers with 2-digit years when formatting network mail. This is because at the time the code was written, RFC822 demanded 2-digit years for compatibility purposes. However, that requirement has long since gone away and network mailers now use 4-digit years, so this code should be fixed.

[Eric Swenson]

​https://s3.amazonaws.com/eswenson-multics/public/mcrs/MCR10168.pdf