Rename zinc_analysis_file to zinc_analysis_collection.

To avoid confusion with the new zinc analysis file code to come...
New zinc analysis read/write code.
Get rid of a lot of zinc-related dead code .
Use native split/merge/rebase.
Get rid of TransformingArtifactCache.

It doesn't do anything useful now that we rebase in Python.
Get rid of more no-longer-needed zinc cruft.
Start getting rid of ZincAnalysisCollection.
Get rid of the old dependency analysis code.