1.7 Superseding

The message-supersede command pops up a message buffer that will supersede the message in the current buffer.

Headers matching the message-ignored-supersedes-headers are removed before popping up the new message buffer. The default is
`^Path:\\|^Date\\|^NNTP-Posting-Host:\\|^Xref:\\|^Lines:\\|
^Received:\\|^X-From-Line:\\|Return-Path:\\|^Supersedes:'.