Previously, if a Range request came back 200 OK (rather than 206 Partial
Content), we would mangle the response body. This could happen if there
was a middleware that would silently drop Range headers, for example.
Now, if the response does not include a Content-Range header, we will
log a warning and seek to our previous position in the stream. If the
Content-Range header has an unexpected value, we will raise an exception.
Change-Id: I94d4536cc1489968d45a2b6ba7edd70c85800275
fd5579a154