Fix handling of paths when run outside the repo.
The main problem was that dirstate.getcwd() returned just "",
which was interpreted as "we're at the repo root". It now returns
an absolute path.
The util.pathto function was also changed to deal with the "cwd is
an absolute path" case.
#!/bin/sh
hg init
echo 123 > a
hg add a
hg commit -m "first" -d "1000000 0" a
mkdir sub
echo 321 > sub/b
hg add sub/b
hg commit -m "second" -d "1000000 0" sub/b
cat sub/b
hg co 0
cat sub/b 2>/dev/null || echo "sub/b not present"
test -d sub || echo "sub not present"
true