Since datagrids must render each and every cell, we do a bunch of
optimizations to prevent all the expensive template machinery from
running on each render. We cached the contents of a RequestContext,
turning it into a standard Context, and overrode the variables. This
prevented a bunch of template context stack manipulation and data
fetching.

In Django 1.8, the template support has been rewritten for multiple
backends. Now, a RequestContext is empty until bound to a template,
which happens just before the render, and cleared just after. Now,
instead of a RequestContext being populated once during instantiation,
it's populated for each template, making it really expensive. It also
just didn't work.

We now create a dummy template and manually bind the RequestContext to
it. This gives us a populated RequestContext we can work with.

The datagrid works again on both Django 1.6 and 1.8.