The related object widgets call build_attrs in order to create some

attributes to pass into the HTML for the widgets. Django's changed the

signature for this method since Django 1.6, which led to some crashes

during rendering.
The function itself is really simple in its purpose, so rather than

working around the changes, we just build the attributes dictionary in

the widget directly, fixing that compatibility problem.

Unit tests pass on Django 1.6 and 1.11 (with other in-progress changes).