bug#20206: 25.0.50; [PATCH] keep diff-mode's window visible when we visit sources from diff-mode

[Eli Zaretskii]

> From: Dima Kogan <dima@secretsauce.net>
> Date: Thu, 26 Mar 2015 11:25:27 -0700
> 
> When looking at a patch in diff-mode, one can visit the sources being
> patched with several functions, for instance (diff-goto-source). This
> patch makes sure that the source buffer does not cover up the diff-mode
> buffer in its window, but uses any other window instead.

IMO, this should be controlled by a user option, since we can never be
sure there isn't someone who likes the current behavior.  Not having
an option will not allow them to get the old behavior back, which IMO
is not a good idea.

Thanks.