rust-dirstate-status: add call to rust-fast path for `dirstate.status`
The reasoning behind this patch is explained in the first patch of the series.
Differential Revision: https://phab.mercurial-scm.org/D7060
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.