title: python multiprocessing pipe poll bug
body: <p>Using pipes for process communication with the multiprocessing library I noticed some strange behaviour of the poll function. If I close the other end of the pipe poll() returns true which is kind of odd. The python docs dont really tell what to expect. Still I was thinking poll() would at least return false if there is definitely nothing in the pipe and the other end is even closed. I use python3.3.2 but it seems to be the same for python 2.7.5. Is this intended or a bug and if it´s not a bug what is it good for?</p>
  
  <pre><code>import multiprocessing
  
  if __name__ == '__main__':
  
      con = multiprocessing.Pipe(True)
      con1, con2 = con
  
      print(str(con1.poll())) #prints False
      con2.close()
      con1.close()   
  
      con = multiprocessing.Pipe(True)
      con1, con2 = con
  
      con2.close()
      print(str(con1.poll())) #prints True
      con1.close()
  </code></pre>