Checkpoint a tiny bit of thinking about a better treeseq_safe pred.  Generation numbers are missing.
Checkpoint a tiny bit of thinking about a better treeseq_safe pred.  Generation
numbers are missing.

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl