dirstate: make dir collision logic faster
- shortcircuit decpath if we haven't built the _dirs map
- increment only for leafnodes of directory tree
(this should make construction more like O(nlog n) than O(n^2))
Is there an error message when trying to diff non-existing files?
found: No such file or directory
not: No such file or directory
Is there an error message when trying to add non-existing files?
found: No such file or directory
not: No such file or directory