Shift path fragments from PATH_INFO to SCRIPT_NAME and vice versa.

           :param shift: The number of path fragments to shift. May be negative
                         to change the shift direction. (default: 1)

def path_shift(self, shift=1):
        ''' Shift path fragments from PATH_INFO to SCRIPT_NAME and vice versa.

           :param shift: The number of path fragments to shift. May be negative
                         to change the shift direction. (default: 1)
        '''
        script_name = self.environ.get('SCRIPT_NAME','/')
        self['SCRIPT_NAME'], self.path = path_shift(script_name, self.path, shift)
        self['PATH_INFO'] = self.path