title: How to recursively compute Delayed in collection
body: <p>I am a new user to try dask delayed. I want to use delayed to automatically transform function and code into Delayed. However, I found delayed.compute didn't recursively compute Delayed in collection... </p>
  
  <pre><code>from dask import delayed, base
  
  @delayed
  def inc(x):
      return x + 1
  
  @delayed
  def colls(ind):
      return [inc(i) for i in xrange(ind)]
  
  
  data2 = colls(2)
  data2.compute() # I expect [1, 2], but get [Delayed('inc-...'),
   Delayed('inc-...')]
  </code></pre>
  
  <p>Did I missing any thing to make it work or Dask.delayed doesn't support it?</p>