Add a permission to control access to report form

I'm currently integrating Privatemsg with Mollom, see #720038: Mollom integration. As usual, with private messages, everything is a bit different than with "public" content like comments/nodes (even if they are not visible to everyone). Adding protection to the form works perfectly and so does adding a "report to mollom" link. But there are two remaining issues:

- Currently, when you delete a private message, you are then redirected back to the thread unless you've deleted the last message of that thread, then you are redirected back to /messages, the messages list. However, the Cancel link should always return to the thread because there is always at least one message left. I want to do the same with the report to mollom feature. Adding a #value element for the delete destination is easy with hook_form_alter(), but I can't access it from my report delete callback so I'd have to add a custom submit callback.

- Deleting a message does by default only delete it for the current user, unless he has the 'read all private messages' permission, which allows to read and delete messages for other users. Then an additional option is added to the confirmation form which allows to delete the message for all recipients. Again, I'd like to do the same for report to mollom and as before, adding the option to the form is easy, thanks to hook_form_alter(). But this time, I really need the information in my report delete callback because I have to decide there for whom the message needs to be deleted. The only alternative is to replace the default submit callback with a custom one but I don't like that at all. *

Proposal:

So, what I'm suggesting exactly is passing $form_state['values'] as the third parameter to the report delete callback. This would be a one line patch and would not break compatibility with existing modules. I can write a patch, just wanted to ask for feedback first.

* Note: I think giving a normal user that can only delete a message for himself the report to mollom permission is a bad idea, it would be better if he would just be allowed to flag a message as possible spam and let an admin review it. But that would require either a separate feature, including a list of flagged messages or integration with flag/views (we don't have that yet, except for adding a contact link to a user/node view). Any suggestions?