Make differential.querydiffs more liberal about arguments

Summary:
Fixes T12092. D17164 made DiffQuery more strict about arguments using modern conventions, but differential.querydiffs uses bizarre ancient conventions.

Give it more modern conventions instead.

Test Plan: Made a querydiffs call with only revision IDs.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12092

Differential Revision: https://secure.phabricator.com/D17172