bug#32939: 27.0.50; Don't reject confusable quotes, just fontify & mention them in error messages

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Date: Thu, 04 Oct 2018 19:58:10 -0400
> 
> As a followup from [1], here is a patchset which replaces the master's
> current rejection of confusable quotes on `read', and instead adds a
> hint to the error message when evaluating an expression with a
> confusable quote leads to an error.
> 
> And also highlight such quotes with warning-face.

Thanks.  If this is accepted, it will need documentation changes,
including NEWS.