bug#21998: Run 'make change-history' on release branch

[Eli Zaretskii <eliz@gnu.org>]

> From: Richard Stallman <rms@gnu.org>
> CC: rgm@gnu.org, 21998@debbugs.gnu.org
> Date: Wed, 09 Mar 2016 11:38:24 -0500
> 
> I am trying to understand the situation from what I read in some of
> these messages.  If the ChangeLog files are only generated from the
> Git log mssages, which cannot be corrected, then how does fixing ChangeLog
> entries work?

We fix the generated ChangeLog.  The person who makes a mistake is
supposed to invoke "make change-history", which updates the file
ChangeLog.2 with the log messages of the recent commits (by running
Git with a suitably computed command line), and then edit the updated
file and commit the result.  "make change-history" incrementally
updates ChangeLog.2, so the next time it is invoked, only the later
commits will be added to the file.

This worked, more or less, as long as we only developed on master
(except that not everyone who made mistakes bothered to correct them).
But as soon as we started to work on both master and the release
branch, this broke down because merges from the release branch to
master don't live well with the manual corrections.  This was never
fixed because there appears to be no motivation for fixing it.