windows: avoid deleting non-empty reparse points
If a hg repository including working directory is a reparse point (directory
symlinked or a junction point), then using os.removedirs will remove the
reparse point erroneously. This is fixed by only removing directories if they
are empty.
adding base
foo/renamed
renamed
bar/renamed
renamed
baz
.hg/patches/baz
% test patch being renamed before committed