fix #38 check that path doesn't increase in length
fix #38 check that path doesn't increase in length

py.path.local.dirname returns an empty string for '/'.dirname
and py.path.local('') returns the current directory so you
have to be careful to traverse directories by checking that
the path never increases when going up the tree
See https://github.com/pytest-dev/py/issues/220 for details

radiasoft/pykern,radiasoft/pykern