The recent changes to switch to the compatibility functions for

loading/rendering templates broke datagrids, due to an argument that was

ultimately left out of the implementation of render(). The datagrid

was trying to render without using a RequestContext, since it already

created a slimmed-down context containing necessary request information

in order to avoid performance penalties.
This updates the call to explicitly use render_to_string() instead, so

that we can avoid RequestContext, and returns an HttpResponse for

that rendered content.

Verified that the dashboard loads again.