This is a spike adding support for patch series.  It's just a starting point for discussion, not a serious patch yet.  I'll post about it on the reviewboard-dev mailing list.

Depends on #2490 (djblets).  rbtools #2492 lets you post a patch series review request.

As well as all the "XXX" comments and a stray print or two, there are a few bits of dead code in here, and a dead test I think: sorry.  It's not worth anybody's time looking closely at the details of this patch at this stage anyway, so I didn't bother to fix these.

Very little!