integration tests do not need to load fixtures by hand

I don't know when this changed, checked back up to 3.2 and integration
tests instantiate fixtures just fine.
Update all Rails 4.1.0 references in guides to 4.1.1 [ci skip]
Merge pull request #15304 from JohnKellyFerguson/guides-4.1.1

Update all Rails 4.1.0 references in guides to 4.1.1 [ci skip]
unwrap the constraints object on initialization, eliminate loops

Unwrap Constraints objects.  I don't actually think it's possible
to pass a Constraints object to this constructor, but there were
multiple places that kept testing children of this object.  I
*think* they were just being defensive, but I have no idea.