Support the Object Storage Service If-None-Match header

* Change the default number of automatic retries in the event of an error status to 0. This improves the performance of many calls which use 400+ status codes for some expected ("success") cases. This does not change the retry behavior in response to an authentication failure.
* Fixes #402
@alanquillin Do you foresee any problem with this change (rationale given in the pull request)?