Add more private declarations.

These are "private" declarations I'd added locally while trying to understand things, and figure I would submit them, if anything because I kept getting trivial conflicts each time I'd pull in master.

I was going to see if Shark used any of these methods, but sbt is being uncooperative--I don't really know how the Shark/Spark integration works, but admittedly I'm touching DAGScheduler and friends here, which is pretty core, so I suppose I would not be surprised if some of it is used.

Perhaps if this does break Shark, the offending methods could be explicitly documented as "used by shark", just as a hint to otherwise-unaware readers like me that it really is a public contract.