views: get_request_body: decode the request's body
views: get_request_body: decode the request's body

This change ensure that the return request body is unicode (str in
Python 3).  This is desired because, e.g., `json.loads()` requires that
the the data be `str` in Python 3.

davidfischer/rpc4django,davidfischer/rpc4django,davidfischer/rpc4django