Cleanup PhaseAssembly/DependencyGraph/Node
Cleanup PhaseAssembly/DependencyGraph/Node

Nothing particularly important.  Was just reviewing/studying, and here
there were a number of improvments so I thought it was worth proposing.

lrytz/scala,lrytz/scala,lrytz/scala,scala/scala,scala/scala,scala/scala,lrytz/scala,scala/scala,lrytz/scala,lrytz/scala,scala/scala,scala/scala