Cleanup of ambiguous treatment of source-tree vs. multitree IDs
Cleanup of ambiguous treatment of source-tree vs. multitree IDs

These were causing subtle bugs in the tree-building logic, since we were sometimes relying on the fact that most multitree IDs are als source (NCBI) IDs.

NESCent/FossilCalibrations,NESCent/FossilCalibrations,NESCent/FossilCalibrations