Comment 14 for bug 415508

My attached branch changes bzrlib.commit to not use path_contents_summary. It adds a new tree method get_kind_and_executable_from_path so that we can observe the kind and execute bit in one stat call, but so that we don't promise to do any more work than that.

I still need to add a test for that new method, deprecate path_contents_summary, and fix up the TreeTransform use of that method.