Fix post revision action link by getting the adjacent revision

Taking another stab at #585, this time using a workaround that finds the adjacent revision ID.

Unfortunately, the `revision_id` being saved as record meta is still incorrect. But this PR does fix the action link problem to arrive to the correct revision for that record.

![screen shot 2014-11-13 at 9 27 30 pm](https://cloud.githubusercontent.com/assets/522158/5040894/e7cf2fec-6b7b-11e4-927b-4402758f1013.png)

@shadyvb please review.
@shadyvb Nice suggestions. How's this? https://github.com/wp-stream/stream/commit/a0e42d2631aabd15e6e3edbe816b3656fe4d3a7e