bug#22978: 25.0.92; log-view-diff: TMM required for non-consecutive revisions

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Date: Wed, 20 Jun 2018 00:00:25 -0400
> Cc: 22978@debbugs.gnu.org
> 
> > The patch included at the bottom restores the original behavior for us
> > non-TMM users while keeping TMM behavior.
> 
> Not sure if it makes sense to change this.

My problem with the change is that there seems to be no escape from
it.  And since in any buffer, the mark gets set pretty soon after one
starts to move around, it means users who turn off transient-mark-mode
will have no reasonable way of diffing the revision at point with the
previous one.  By contrast, the current behavior allows you to get
diffs between revisions at region edges by "C-SPC C-SPC" etc.