tests/test-dirstatedirs

setup: use sys.executable to call hg

Executing ".\hg" does not work on Windows, but we can instead ask
Python to execute hg.

#!/bin/sh

# test dirstate._dirs refcounting
hg init t
cd t
mkdir -p a/b/c/d
touch a/b/c/d/x
touch a/b/c/d/y
touch a/b/c/d/z
hg ci -Am m
hg mv a z