The new rbt patch implementation did a pretty good job of applying

commits from new-style review requests that have multi-commit history,

but it broke with old review requests that just have single diffs. This

change fixes up the issues I ran into:

The code was never populating the commits list, unless --squashed

  was given. It then would always use commits[0], blowing up. I've

  changed it to fetch the full diff data when there are no commits.
When --squashed was specified, we'd end up passing expand=None to

  the API request, which would then blow up.
The code that determined whether to create the commit wasn't working

  properly with --squashed, because it was testing patch_num as if it

  was 0-indexed when in fact it's 1-indexed.

Was able to apply patches from review requests without commit history.
Was able to apply patches using --squashed
Ran unit tests (there are some problems with the test suite right now

  but those are unrelated to anything touched here).