Merge branch 'kn/osxkeychain-idempotent-store-fix'

An earlier check added to osx keychain credential helper to avoid storing the credential itself supplied was overeager and rejected credential material supplied by other helper backends that it would have wanted to store, which has been corrected. * kn/osxkeychain-idempotent-store-fix: osxkeychain: avoid incorrectly skipping store operation