The recent work to refactor the diff fragment rendering code and the

view broke diff expanding, due to the lack of a **kwargs in

process_diffset_info(), and a captured URL parameter name that wasn't

updated. This affected both diffs and interdiffs, with slightly

different breakages.
The **kwargs argument has been added, and the URL capture name fixed,

restoring expansion support.

Expansion worked again, for both diffs and interdiffs.