Handle tuple returns from get_sort_field()

Review Request #10278 — Created Oct. 25, 2018 and updated — Latest diff uploaded

Information

Djblets
release-2.0.x
d0adbe5...

Reviewers

This fix enables handling of tuples as returns from a Column's
get_sort_field() during precompute_objects(). This is related to
the "Make all columns sortable on /users/ page" fix.

All tests pass for Djblets.