Edit and add old WYM class back in, fix expression to behave as
intended.

Since jquery 1.4, the [@attr] has been deprecated
(@cite: http://api.jquery.com/category/selectors/attribute-selectors/)

causing the exclusive selection in the texteditor not to work as
demonstrated in settings file.  More confusingly, without the
"important" example, it's not at all obvious why the selector is
excluding hidden-note.

Note:  You still can't actually see this working without including
appropriate classes in your template pages, and I'm not 100% confident
that the WYM_STYLESHEET is working.