Major Description
A bug report on the user list drove me to revisit some of the core planning logic, particularly around how we decide where to split up DoFns between two dependent MapReduce jobs.
I found an old TODO about using the scale factor from a DoFn to decide where to split up the nodes between dependent GBKs, so I implemented a new version of the split algorithm that takes advantage of how we've propagated support for multiple outputs on both the map and reduce sides of a job to do finer-grained splits that use information from the scaleFactor calculations to make smarter split decisions.
One high-level change along with this: I changed the default scaleFactor() value in DoFn to 0.99f to slightly prefer writes that occur later in a pipeline flow by default.
