requests_kerberos breaks requests.Response.elapsed

[JacobHenner]

requests.Response has an elapsed attribute, which records "the amount of time elapsed between sending the request and the arrival of the response".

When requests-kerberos is used for auth, the value stored in that attribute is incorrectly set to timedelta(0), instead of the actual request time. The value from the initial request is lost here.

Instead, I believe elapsed should account for the total time elapsed - the sum of elapsed for all responses until the final response is received (the one which is returned to the caller). It should never return timedelta(0).