Traverses children, building a path based on relation <rel>, until given path is found.

def findByPath(self, rel, path):
        """Traverses children, building a path based on relation <rel>, until given path is found."""
        if((path=="") or (path=="/")):
            return(self)
        (front,dummy,rest) = path.lstrip("/").partition("/")
        for child in self.items:
            if front in child.values(rel):
                return child.findByPath(rel, rest)
        return None