rhg: remember the inode of .hg/dirstate This allows us to detect changes of `.hg/dirstate`, which is either the full dirstate (in dirstate-v1) or the docket file (v2) without relying on data inside the file. It only works on UNIX systems. This fixes a race condition for dirstate-v1 (as demonstrated by the test changes) and adds a confortable layer of sanity for dirstate-v2.