'Load a manifest at path or return a suitable manifest already loaded.'

def load(self, path):

    path = os.path.normpath(path)
    mtime = os.stat(path).st_mtime
    if ((path not in self) or (self[path].mtime != mtime)):
        manifest = self.build(path)
        self[path] = self.manifest_mod(manifest, mtime)
    return self[path].manifest
