Add error for debugging

Author: g3xzh

src/libextra/stats.rs

@@ -1116,7 +1116,9 @@ mod tests {
     #[should_fail]
     fn test_sum_overflow_f64() {
         let n = f64::MAX_VALUE;
-        [n, -n, n, n / 10.0].sum();
+        println!("{} ", [n, -n, n, n / 10.0].sum());
+	println!("{} ", [n, -n, n, 0.1 * n].sum());
+	error!("n {} ; sum {}", n, [n, -n, n, n / 10.0].sum())
     }
 }