dirstate: set identity whenever we read the dirstate's v2 docket
The docket can be loaded outside of a full read (for exemple when
pre-fetching parents), so the current code would read/set the identity
after loading the data, opening a race condition:
A0: first process docket is read
B0: other process appends new data to the dirstate (and changes the docket)
A1: first process sets the identity (based on pre-B content, but with post-B identity)
A1: first process loads the dirstatemap from the data file
A1: first process does not detect the race and overwrites the update from B.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.