timers: give Timeouts a constructor name

Refs: https://github.com/nodejs/node/pull/5792
PR-URL: https://github.com/nodejs/node/pull/5793
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>

lib/timers.js

@@ -439,7 +439,7 @@ exports.clearInterval = function(timer) {
 };
 
 
-const Timeout = function(after) {
+function Timeout(after) {
   this._called = false;
   this._idleTimeout = after;
   this._idlePrev = this;

test/message/timeout_throw.out

@@ -2,6 +2,6 @@
   undefined_reference_error_maker;
   ^
 ReferenceError: undefined_reference_error_maker is not defined
-    at ._onTimeout (*test*message*timeout_throw.js:*:*)
+    at Timeout._onTimeout (*test*message*timeout_throw.js:*:*)
     at tryOnTimeout (timers.js:*:*)
     at Timer.listOnTimeout (timers.js:*:*)