With this patch post-review will support the revision-range option following the syntax explained here [1].

[1] http://www.review-board.org/docs/manual/dev/users/tools/post-review/#posting-committed-code

I have tested this new feature locally and it works fine.

I have successfully tested the following commands:
post-review --revision-range=rev1:rev2 --guess-summary --guess-description
post-review --revision-range=rev1:rev2 --guess-description
post-review --revision-range=rev1:rev2
post-review --revision-range=rev --guess-summary --guess-description
post-review --revision-range=rev