Speed up rbt post -u.
rbt post -u, in an effort to match draft summaries, was fetching every

opened draft for a user individually and pulling info from them. This

was slow, particularly with lots of pending review requests.
Now it uses the field expansion support in the API to fetch drafts in

one go, reducing the number of calls significantly.

Ran with --debug and saw that it wasn't fetching drafts anymore.
Tested with and without pending drafts. It matched correctly.