Problem: `sync-tup-ctime.py` realigned every node's ctime, which hid real source changes whose Tupfile didn't change. Fix: stamp the cache with its commit and on restore, `git diff` against it, keeping changed files dirty so tup rebuilds them. Reviewed-on: #525 Reviewed-by: Mikhail Frolov <mixa.frolov2003@gmail.com> Reviewed-by: Gleb Zaharov <risdeveau@lair.moe>