add --parent-diff-filename option to rbt post

Review Request #9783 — Created March 15, 2018 and updated — Latest diff uploaded

Information

RBTools

Reviewers

rbt post has the ability to create a review with a "parent" diff, but there's no option to provide one. This patch adds it.

I have successfully created a review in our company's RB installation using an rbt with this patch.