Dean Stringer submitted the attached patch.

I reviewed the code, it looks good, just two issues:

1. There isn't a change to editcomment.php, which probably indicates that it was missing this security check in the first place. SIGH. Probably if altering the area we should fix it.

2. If possible, the form should probably include the necessary disabledIf so that the new element is only enabled if group mode is 'visible'.

I did also wonder whether anyone would want the option off, but then decided maybe they would...