tests/test-dirstatedirs

Fix up rebase's handling of strip backups

#!/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