Return an XMLSchema instance loaded from the given file.
           filename -- name of file to open

def loadFromFile(self, filename):
        """Return an XMLSchema instance loaded from the given file.
           filename -- name of file to open
        """
        if self.__base_url:
            filename = basejoin(self.__base_url,filename)
        file = open(filename, 'rb')
        try:
            schema = self.loadFromStream(file, filename)
        finally:
            file.close()

        return schema