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

[Eli Zaretskii]

> From: Stephen Berman <stephen.berman@gmx.net>
> Cc: 15841@debbugs.gnu.org
> Date: Mon, 11 Nov 2013 15:12:15 +0100
> 
> This change broke dired-maybe-insert-subdir.  Perhaps this should be a
> new bug number, but since part of the breakage is display-related, I
> decided to report it here.  To reproduce:
> 
> 0. emacs -Q (built from trunk bzr 115033 or later)
> 1. Open a directory in Dired, e.g. the Emacs source tree root.
> 2. Put point on an entry listing a directory, e.g. admin.
> 3. Type `i'.
> => Emacs hangs.

Actually, if you rebuild with assertions (--enable-checking), Emacs
hits an assertion violation before it starts inflooping, and aborts.