title: blob_send save_as=True fails after converting from db to ndb
body: <p>I converted <a href="http://blog.notdot.net/2010/03/Implementing-a-dropbox-service-with-the-Blobstore-API-Part-1" rel="nofollow">nicks blog</a> example to ndb
  now this line fails:</p>
  
  <pre><code>self.send_blob(file_info.blob, save_as=True) 
  </code></pre>
  
  <p>with this error:</p>
  
  <pre><code>ValueError: Expected BlobInfo value for blob_key_or_info.
  </code></pre>
  
  <p>Rest of the class:</p>
  
  <pre><code>class FileDownloadHandler(blobstore_handlers.BlobstoreDownloadHandler):
     def get(self, file_id):
         file_info = models.FileInfo.get_by_id(long(file_id))
  
  if not file_info or not file_info.blob:
    self.error(404)
    return
  
  self.send_blob(file_info.blob)
  #self.send_blob(file_info.blob, save_as=True)
  </code></pre>
  
  <p>Why did the result change?</p>