Add utils.inherits. Make User inherit EventEmitter.

utils.inherits is the Node.js impl but with the addition of a polyfill for
Object.create().

lib/utils.js

@@ -157,3 +157,95 @@ module.exports.checkObjectHasNoAdditionalKeys = function(obj, allowedKeys) {
         }
     }
 };
+
+/**
+ * Inherit the prototype methods from one constructor into another. This is a
+ * port of the Node.js implementation with an Object.create polyfill.
+ *
+ * @param {function} ctor Constructor function which needs to inherit the
+ *     prototype.
+ * @param {function} superCtor Constructor function to inherit prototype from.
+ */
+module.exports.inherits = function(ctor, superCtor) {
+    // Add Object.create polyfill for IE8
+    // Source:
+    // https://developer.mozilla.org/en-US/docs/Web/JavaScript
+    // /Reference/Global_Objects/Object/create#Polyfill
+    if (typeof Object.create != 'function') {
+      // Production steps of ECMA-262, Edition 5, 15.2.3.5
+      // Reference: http://es5.github.io/#x15.2.3.5
+      Object.create = (function() {
+        // To save on memory, use a shared constructor
+        function Temp() {}
+
+        // make a safe reference to Object.prototype.hasOwnProperty
+        var hasOwn = Object.prototype.hasOwnProperty;
+
+        return function(O) {
+          // 1. If Type(O) is not Object or Null throw a TypeError exception.
+          if (typeof O != 'object') {
+            throw new TypeError('Object prototype may only be an Object or null');
+          }
+
+          // 2. Let obj be the result of creating a new object as if by the
+          //    expression new Object() where Object is the standard built-in
+          //    constructor with that name
+          // 3. Set the [[Prototype]] internal property of obj to O.
+          Temp.prototype = O;
+          var obj = new Temp();
+          Temp.prototype = null; // Let's not keep a stray reference to O...
+
+          // 4. If the argument Properties is present and not undefined, add
+          //    own properties to obj as if by calling the standard built-in
+          //    function Object.defineProperties with arguments obj and
+          //    Properties.
+          if (arguments.length > 1) {
+            // Object.defineProperties does ToObject on its first argument.
+            var Properties = Object(arguments[1]);
+            for (var prop in Properties) {
+              if (hasOwn.call(Properties, prop)) {
+                obj[prop] = Properties[prop];
+              }
+            }
+          }
+
+          // 5. Return obj
+          return obj;
+        };
+      })();
+    }
+    // END polyfill
+
+    // Add util.inherits from Node.js
+    // Source:
+    // https://github.com/joyent/node/blob/master/lib/util.js
+    // Copyright Joyent, Inc. and other Node contributors.
+    //
+    // Permission is hereby granted, free of charge, to any person obtaining a
+    // copy of this software and associated documentation files (the
+    // "Software"), to deal in the Software without restriction, including
+    // without limitation the rights to use, copy, modify, merge, publish,
+    // distribute, sublicense, and/or sell copies of the Software, and to permit
+    // persons to whom the Software is furnished to do so, subject to the
+    // following conditions:
+    //
+    // The above copyright notice and this permission notice shall be included
+    // in all copies or substantial portions of the Software.
+    //
+    // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+    // OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+    // MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+    // NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+    // DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+    // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+    // USE OR OTHER DEALINGS IN THE SOFTWARE.
+    ctor.super_ = superCtor;
+    ctor.prototype = Object.create(superCtor.prototype, {
+        constructor: {
+            value: ctor,
+            enumerable: false,
+            writable: true,
+            configurable: true
+        }
+    });
+};