I like this change, however, it's not backwards compatible with older versions of mongoengine's user model.  If I recall the `.has_perm` was added after this project had been in the wild for some time, here: https://github.com/MongoEngine/mongoengine/commit/4b2ad254057a440c2a45016fe8da3318837fb440

We support back to 0.5.2 according to the docs.  I'm okay with the update, but we'd have to acknowledge we no longer support the older version, which to me is at least a minor version bump.  @pydanny   what are your thoughts?