bug#29198: Cursor fringe arrow indicator not updating.

[Keith David Bershatsky]

Thank you, Eli.

I have tested the patch with a current version of Emacs 26 branch and am able 
to verify that this feature is working well, and the prior issue with the lag 
has been rectified.

Great job!

Keith

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DATE:  [11-09-2017 08:29:14] <09 Nov 2017 18:29:14 +0200>
FROM:  Eli Zaretskii <eliz@gnu.org>
> 
> * * *
> 
> Thanks.  Meanwhile I also arrived at the conclusion that this is a
> bug, because the same recipe does work on TTY frames.
> 
> Of course, reverting the above changes is not the solution, because as
> you yourself noticed, it caused redisplay to be significantly
> snappier.  The problem with those changes is that they opened the path
> for the code to use redisplay optimizations when overlay-arrows are
> displayed, which (the optimizations) are incompatible with
> overlay-arrow display.  So the correct solution would be to disable
> those optimizations when overlay-arrows are displayed in the buffer.
> Which I just did.
> 
> Thanks.