gpython should treat standard input as a file, not as input to the REPL

This definition works:

    class X(object):
      def __init__(self, x):
        self.x = x
      def __str__(self):
        return "my name is %s" % self.x

This doesn't:

    class X(object):
      def __init__(self, x):
        self.x = x

      def __str__(self):
        return "my name is %s" % self.x

Both are accepted by C Python.