Always define $form['project'] in the release node form, even when editing releases

There are lots of cases where you need the project node that a release belongs to. In fact, we already node_load() it in project_release_node_form() ourselves in both cases. However, we only stash it in the form when adding a new release. This seems silly. I'd like to just always define it so people altering the release node form can always get to the project without any special cases.