Subject: bug#20290: 25.0.50; Use unified diff format by default, and recommend using it in reports and patches

From: Dmitry Gutov <[email-masked]>
Date: Thu, 09 Apr 2015 23:05:42 +0300

That should involve changing the default `diff-switches' value and small
changes to doc/emacs/files.texi and doc/emacs/trouble.texi.

Let me know if I missed something.

Barring any objections, I'll do that tomorrow-ish, on master.