Attempted implementation of AsgiRequest._stream

[DanLipsitt]

This is the beginning of an attempt to fix #32. It isn't working. This PR is just for the sake of discussion.

The test I added surfaces an issue I mentioned in #66. AsgiRequest uses dict-style access on Message, but Message does not support it. See below. This could be because my test is wrong.

$ python runtests.py 
Creating test database for alias 'default'...
EEE
======================================================================
ERROR: test_stream_is_readable (channels.tests.test_handler.TestAsgiRequest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/dan/src/channels/channels/tests/test_handler.py", line 14, in test_stream_is_readable
    request = AsgiRequest(message)
  File "/Users/dan/src/channels/channels/handler.py", line 25, in __init__
    self.reply_channel = self.message['reply_channel']
TypeError: 'Message' object is not subscriptable

[andrewgodwin]

Ah, yes, message in AsgiRequest is meant to just be the raw underlying message dict from ASGI - see here: https://github.com/andrewgodwin/channels/blob/master/channels/handler.py#L208 where it passes Message.content into the view system, which is the raw dict.

[DanLipsitt]

OK, maybe working now.

[DanLipsitt]

Running up against missing BaseChannelBackend now, so I think that's all I can do for the moment.

[andrewgodwin]

Ah, that shouldn't be needed anymore. Might be old broken test code - this is why I don't want to write more tests until the new architecture is stable :)

[DanLipsitt]

I don't think it has anything to do with the test code. Filed as #69.

[andrewgodwin]

I implemented _stream basically this exact way, so closing!