looks like setting ExposeHeaders has no effect on requests to s3 (headers such as `x-amz-version-id` don't reach the clients) for browser-based uploads. 

http://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectPOST.html
def setUp(self):
        self.s3_client = aws_stack.connect_to_service('s3')
        self.sqs_client = aws_stack.connect_to_service('sqs')
    def test_bucket_policy(self):
        
        self.s3_client.create_bucket(Bucket=TEST_BUCKET_NAME_WITH_POLICY)
        
        policy = {
            'Version': '2012-10-17',
            'Statement': {
                'Action': ['s3:GetObject'],
                'Effect': 'Allow',
                'Resource': 'arn:aws:s3:::bucketName/*',
                'Principal': {
                    'AWS': ['*']
                }
            }
        }
        response = self.s3_client.put_bucket_policy(
            Bucket=TEST_BUCKET_NAME_WITH_POLICY,
            Policy=json.dumps(policy)
        )
        self.assertEqual(response['ResponseMetadata']['HTTPStatusCode'], 204)
        
        saved_policy = self.s3_client.get_bucket_policy(Bucket=TEST_BUCKET_NAME_WITH_POLICY)['Policy']
        self.assertEqual(json.loads(saved_policy), policy)
    def test_s3_put_object_notification(self):