Spaces OG Book

Replaces book adding of book elements to node form with one that is restricted to the current organic group, with the intent of not loading every, single, book structure on every single node form (which book.module is want to do, if a user has administer book outline permission). To install, do as normal than grant users 'add content to group books' permission and remove 'add content to books' and 'administer book outline' permission.

It does not actually require spaces, just that og_get_context will return the group on both node/add and node edit forms.