Emacs 26.1 release branch created

[Eli Zaretskii]

I've created a new emacs-26 branch which will be used to release Emacs
26.x, starting with Emacs 26.1.  This branch should be used for fixing
bugs; new development should continue on master.  (If there are
features that are already on the branch, and their developers want to
put a few finishing touches or additions to those features, please ask
here before pushing further changes that are not bugfixes.)

Alan, you will probably want to cherry-pick your latest commit from
master master to this branch.

Nicolas, please produce the first pretest in, say, a week's time.
Let's optimistically call that pretest 26.0.90.

Thanks.