"Autoseal" comments on selected content types

I wanted to be able to automatically seal comments on a given comment type. I went ahead and rolled a patch of the changes I made, in case you're interested in incorporating it into the module.

To use this feature, go to the content type administration page (admin/content/node-type/foo). In the comments fieldset, this patch adds an option to automatically seal all comments for that content type. Choose 'Seal comments automatically'. That's it.

When someone goes to comment on a node of type foo, this patch alters the comment form to set $form['sealed'] to 1 (TRUE) and eliminates the 'Seal this comment' checkbox from the form. The comment is automatically sealed.