bug#10200: 24.0.92; Message buffer pops up in new window

[Chong Yidong]

With latest trunk:

emacs -Q
C-x m

The *unsent mail* buffer pops up in a different window.

This is a regression from the behavior in previous version of Emacs, and
it is caused by

  revno: 106557
  committer: Stefan Monnier <monnier@iro.umontreal.ca>
  branch nick: trunk
  timestamp: Wed 2011-11-30 09:52:08 -0500
  message:
  * lisp/gnus/message.el (message-pop-to-buffer): Revert 2011-09-11 change.

What is the rationale for this change?

In GNU Emacs 24.0.92.3 (x86_64-unknown-linux-gnu, GTK+ Version 3.2.0)
 of 2011-12-03 on furball