Generate accesskey parameters in form elements

It would be nice if the appropriate form_*() functions allowed for generation of the accesskey XHTML parameter for elements where it made sense, e.g. fieldset, input, textarea, etc.

One can kludge in an accesskey parameter in the attributes argument (probably), and by hand patch in a "span" to underline or otherwise highlight the access key, but it's all hacks to do it right now.