Some tests fail on mac

[petersont]

I think because temp-directories, and canonicalize both work a little differently on mac (and mac's standard canonicalize might even be broken?)

os::canonicalize_ok_if_relative_path os::canonicalize_ok_if_path_ends_in_dotdot os::canonicalize_ok_if_file_exists os::canonicalize_fails_if_subpath_is_file os::canonicalize_ok_with_dotdot_if_paths_exist os::remove_file_fails_if_node_is_a_directory

I'm working on a change to fix them in a way that dodges the idiosyncrasies of mac os, but keeps the tests meaningful.