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
bucket_name = 'test-bucket-%s' % short_uid()
        self.s3_client.create_bucket(Bucket=bucket_name)
        body = 'something body'
        
        object_key = 'key-by-hostname'
        self.s3_client.put_object(Bucket=bucket_name, Key=object_key, Body=body, ContentType='text/html; charset=utf-8')
        url = self.s3_client.generate_presigned_url(
            'head_object', Params={'Bucket': bucket_name, 'Key': object_key}
        )
        
        response = requests.head(url, verify=False)
        self.assertEqual(response.headers['content-length'], str(len(body)))
        
        self.s3_client.delete_objects(Bucket=bucket_name, Delete={'Objects': [{'Key': object_key}]})
        self.s3_client.delete_bucket(Bucket=bucket_name)
    def test_s3_delete_response_content_length_zero(self):