bug#2608: 23.0.90; `w32-use-visible-system-carat' should be a defcustom

[Jason Rumney]

Drew Adams wrote:
> A visually impaired new Emacs user just asked a question about this
> variable on help-emacs-windows@gnu.org. I had never heard of this
> variable. I see now that it is a defvar, even though it seems to be
> documented as a user "flag". Seems like it should be a defcustom.
>   

It was originally intended as a user option, but code was added to 
automatically set it according to whether screen reading software is in 
use. So it should just do the right thing. Documentation probably needs 
updating to reflect that, and the fact that it is only useful for screen 
reading software, as the user seems to have gotten the idea that it 
might help them even though they don't use such software - in fact Emacs 
drawn cursors are far more useful, as they can be configured to be more 
or less visible as the user requires.