thirdparty: port zope.interface to relative imports By using relative imports, we're guaranteed to get modules vendored with Mercurial rather than other random modules that might be in sys.path. My editor strips trailing whitespace on save. So some minor source code cleanup was also performed as part of this commit. # no-check-commit because some modified lines have double newlines Differential Revision: https://phab.mercurial-scm.org/D2930