treemanifest: make filesnotin() faster Same rationale as the previous change.

treemanifest: make diff() faster Containment checking is slower in treemanifest than it is in manifestdict, making the current diff algorithm O(n log n). By traversing both treemanifests in parallel, we can make it O(n). More importantly, once we start lazily loading submanifests, we will be able to easily skip entire submanifest if they have the same nodeid.

treemanifest: store directory path in treemanifest nodes This leads to less concatenation while iterating, and it's useful for debugging.