Fix get_url_params_except and augment_queryset.
My get_url_params_except method forgot to return the value, which meant that

we'd often see "None" in the URL parameters. I've also changed things a bit to

avoid adding empty query parameters when this method returns nothing.
This also fixes the datagrids code to always call Columns' augment_queryset()

methods. By adding a query string like ?sort=people (which is a non-sortable

column), one could drop the datagrid through a code path where it wouldn't call

augment_queryset, leading to bizarre error messages like this:
'ReviewRequest' object has no attribute 'draft_summary'

This change fixes that up, fixes the obsolete docstring for

post_process_queryset.

Played with a bunch of different sort parameters on various datagrids,

including adding query strings that included non-sortable columns.