Re: vc-modify-change-comment for "modern" backend fix

[Alfred M. Szmidt]

Thanks Eli, and Stefan.

   Note that maybe you don't want "just the commit message text" because
   you may want to preserve extra info such as the `Author:`.

There is I think a very deep hole -- creation time, author, committer,
branch colour, etc, etc, etc.  As it is now, modify-change-comment is
quite specific in what it wants to do.

I'll whip something up ...