The ability to recursively enter embedded interactive Python consoles considered harmful

[tleonhardt]

The ability to enter a 2nd interactive Python console within an existing one via "cmd('py')" isn't helpful and could be harmful.

Recommend detecting if running in an interactive console, bypassing running a new one, and printing an error with something like:

def do_py(self):
    if self._in_py:
        self.perror("Recursively entering interactive Python consoles is not allowed.", traceback_war=False)
        return
    self._in_py = True

    ....
    self._in_py = False
    return self._should_quit