title: Retrieve task result by id in Celery
body: <p>I am trying to retreive the result of a task which has completed.
  <strong>This works</strong></p>
  
  <pre><code>from proj.tasks import add
  res = add.delay(3,4)
  res.get()
  7
  res.status
  'SUCCESS'
  res.id
  '0d4b36e3-a503-45e4-9125-cfec0a7dca30'
  </code></pre>
  
  <p>But I want to run this from another application. So I rerun python shell and try:</p>
  
  <pre><code>from proj.tasks import add
  res = add.AsyncResult('0d4b36e3-a503-45e4-9125-cfec0a7dca30')
  res.status
  'PENDING'
  res.get() # Error
  </code></pre>
  
  <p>How can I retrieve the result?</p>