[OS X Emacs] Emacs 25 Mojave fixes backport

[Elliott Roper]

> On 4 Oct 2018, at 22:33, David Reitter <david.reitter at gmail.com> wrote:
> 
> I back-ported the two macOS Mojave fixes to Emacs 25.
> Please check my handiwork before I push it [1]
> 
> One user reported issues with the cursor leaving traces while scrolling [2], which I reproduced on a pre-Mojave machine, but not on my Mojave system.  I’m unclear whether that is also the case on the 26 branch.  I can try tomorrow unless someone else can comment.
> 
Using last night's nightly and a Mojave iMac Pro, I get the same cursor mouse trail by holding down the up-arrow. It did not appear till the buffer scrolled, fixed itself when down-arrowing over it, and a re-draw forced by bouncing the text size down and back up cleared it too.

Elliott Roper
+44 1663 747334
+44 7454 402200