Fix for incorrect old reference to "nodehash"
Add stubs for API methods for validating and sorting nodes once graph is built
Implemented DEG_graph_validate_links()
Stub for graph sorting
Refining timesource lookup to include the possibility of looking up those for timeoffset
Tweaks to AnimData-building code for how it interacts with the new structure

There are still some rough patches which need further work. Namely
* How to link up to bones...
* Resolving RNA-Pointer links to nodes...
Updating shapekey handling - still many unresolved questions