Provide rules format support

Mis-using this to test the tests...

x.patch queued for re-testing.

I applied the patch manually but I was unable to get it to work. As is, I had to change 'options list' => _privatemsg_rules_filters, to 'options list' => _privatemsg_rules_filters(),, which gives this error: Fatal error: Unsupported operand types in /Volumes/Bullfrog/om/includes/form.inc on line 2623.

When I removed the line return $options and placed a dpm() instead, I can see that the list of input filters is correctly generated; however, for a reason I do not understand, they are not prefilled as options correctly (I get the error with the return statement in place).

In any case, is "format" a property of the private message, or a property of the body of the privatemsg? (Because in theory, couldn't a privatemsg have multiple fields, some of which allow configurable formats and some that do not)?