bug#9571: 24.0.50; user option to turn off bidi, please

[Drew Adams]

> > 1. That's not very user-friendly.  We should have a user option that
> >    does this, i.e., gives users an easy way to disable this 
> >    feature if they don't want to use it.
> 
> Why would we need an option for that other than for debugging 
> purposes?

Uh, to give "users an easy way to disable this feature if they don't want to use
it."

Can you imagine that there are some Emacs users who do not _ever_ need or want
to edit bidirectional text?  Just like there are some users who never need or
want to use SQL code editing features, or image-library features, or Emacs-based
mail, or...

Why make such users figure out that they need to put a `setq-default' in their
.emacs to get back (as much as possible) the traditional behavior (and
possibly/hopefully eliminate some of the bidi overhead)?

I understand that it is apparently hard to make bidi support entirely optional,
e.g., remove all of the overhead even if turned off.  But it has also been
advised that _if_ you want to turn bidi editing off, setting this variable to
nil is the way to do it.

So make it a user option.  Only those users who want to turn it off will turn it
off - what's the problem?  Why not give users that control and ease of control?