Add never delete option to rails 3 paranoia

The default behavior of for `#destroy` will delete a record if it's called twice. It seems a bit silly for `#destroy`'s behavior to change based on the number of calls, but alas that has become the accepted default.

I've added a `:never_delete` option that will make it so `#destroy` never actually deletes a record from the DB. So `#destroy` will update the paranoia column and that's it.

I'm open for changing the `:never_delete` name to match with the paranoia abstraction.. maybe `:uber_paranoid` or something.

Any :thought_balloon:s?