Resque Deltas for TS v1/v2/v3 and Flying Sphinx v1

I've changed a ton here - essentially, it's a rewrite, for a few reasons:

* I really like the idea of locking, but couldn't get it working reliably in tests, so I pulled that out.
* Not sure how the FlagAsDeletedSet was better than a simple FlagAsDeleted job.
* Generally opted for the simplest implementation possible everywhere.
* Cucumber dropped for a few RSpec acceptance tests instead.

All of this is open to discussion - I know this is a massive departure from what you had in place, and it's got me thinking about locking as something that could be a bigger part of Thinking Sphinx indexing generally... although I'm yet to have any inspiration on the best way to implement that.