bug#2689: 23.0.91; Can't customize whitespace-display-mappings: "This field should contain a single character"

[Chong Yidong]

Daniel Clemente <dcl441-bugs@yahoo.com> writes:

> 1. Open emacs -Q, with Emacs from CVS from right now
> 2. M-x customize-variable RET whitespace-display-mappings RET
> 3. Imagine you want to change the $ (which represents newline) to /
> (or anything else) and do this change
> 4. Try to save changes for current session
>
>   You get this error: "This field should contain a single
>   character". And the change isn't saved.

I've committed a fix to trunk.  Thanks for the bug report.