bug#18601: 24.3.94; set-fringe-mode with left fringe 0 breaks window width calculations on Mac OS

[Eli Zaretskii]

> From: Constantine Vetoshev <vetoshev@gmail.com>
> Date: Thu, 2 Oct 2014 12:22:51 -0700
> Cc: 18601@debbugs.gnu.org
> 
> I'm attaching two screenshots which show what happens.

I think this is the result of 1 column being reserved for continuation
glyph on the left (required for R2L lines).  This is a "feature".
Packages that are sensitive to the number of columns in a window
should now account for this even when only the left fringe is zero.