retry 499 error if seen by client (#1627)

retry.go

@@ -110,6 +110,7 @@ func isS3CodeRetryable(s3Code string) (ok bool) {
 // List of HTTP status codes which are retryable.
 var retryableHTTPStatusCodes = map[int]struct{}{
 	429:                            {}, // http.StatusTooManyRequests is not part of the Go 1.5 library, yet
+	499:                            {}, // client closed request, retry. A non-standard status code introduced by nginx.
 	http.StatusInternalServerError: {},
 	http.StatusBadGateway:          {},
 	http.StatusServiceUnavailable:  {},