bug#25767: 25.1.91; abbrev-prefix-mark expansion inserts newline

[Eli Zaretskii]

> From: Allen Li <vianchielfaura@gmail.com>
> Date: Fri, 17 Feb 2017 14:15:07 -0800
> 
> The fix is really easy, but I haven't contributed to Emacs before, so
> I don't know the proper procedure.

The simplest way is to post the patch, as "diff -u output", here.  If
it's small enough, that's all you need.  Bonus points for following
the advice in CONTRIBUTE, which you can find in the Emacs repository
and in new enough release tarballs.  Running the relevant tests in the
Emacs test suite (abbrev-tests.el) to make sure the changes cause no
regressions is also a plus.

> (Also, the existing code really bugs me; I would tear it out and
> replace it with (with-excursion) if Emacs was my pet project that
> millions of users aren't depending on.)

You could post 2 alternative patches (assuming the more radical one
passes all the tests in the test suite), and let us judge.

Thanks.