bug#15841: Display bugs with cache-long-lines non-nil

[Eli Zaretskii]

> From: Andy Moreton <andrewjmoreton@gmail.com>
> Date: Sat, 16 Nov 2013 18:53:31 +0000
> 
> Thanks Eli - I've seen the same problem with inserting a subdirectory in
> a dired buffer. Applying your patch to r115122 fixed dired for me.

Thanks for trying.  I will wait till Monday, to see if no adverse
effects pop up, then commit those changes.