Under certain cases, such as when putting a manifest or check for the existence
of a layer, the status code checks in session_v2.go were too narrow for their
purpose. In the case of putting a manifest, the handler only cares that an
error is not returned. Whether it is a 304 or 202 does not matter, as long as
the server reports success. Having the client only accept specific http codes
inhibits future protocol evolution.
Signed-off-by: Stephen J Day <stephen.day@docker.com>
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