Change status access from header to attribute.

[dhermes]

This is to unify all the times a status is used from the response (containing header info) of an HTTP request.

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@jonparrott @nathanielmanistaatgoogle I was considering adding transport.get_status(response) and transport.get_header(response), these are essentially the only remnants of httplib2 outside of the transport module. (The only other is that http.request returns response, content and that content is always bytes.)

[dhermes]

@jonparrott @nathanielmanistaatgoogle Can you weigh in on transport.get_status(response) and transport.get_header(response)?

[theacodes]

Let's table it until we actually try using a different transport.

[dhermes]

SGTM. I'm more concerned about flagging / fencing off all the httplib2 features.