bug#9771: 24.0.90; Redisplay problems with control characters

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 18 Oct 2011 18:58:41 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 9771@debbugs.gnu.org
> 
> > Date: Tue, 18 Oct 2011 08:56:34 -0400
> > From: Eli Zaretskii <eliz@gnu.org>
> > Cc: 9771@debbugs.gnu.org
> > 
> > Anyway, this being so, I found a way to optimize a couple of expensive
> > loops inside bidi.c for the important special case of a plain L2R text
> > in the buffer.  With these optimizations, the bidi redisplay of the
> > entire window showing a buffer with 2000 binary nulls is only a few
> > milliseconds slower than the unidirectional one.
> > 
> > I will install those changes later today, after some more testing.
> 
> Done (revision 106124 on the trunk).

For the record, revision 106151 speeds up the bidi display in a more
general class of use cases.  (Previously, appending some character,
like `a', to the 2000 nulls in the original example would still slow
down redisplay, even after the changes in r106124.)