Make Utils.js use Object.define to modify Array

Previously, we were modifying Array's prototype using
simple assignment.  This can mess with enumeration/iteration.
Thus, we now use Object.defineProperty with enumerable set to
false.

See #366

include/util.js

@@ -17,30 +17,36 @@ var Util = {};
  * Make arrays quack
  */
 
-Array.prototype.push8 = function (num) {
+var addFunc = function (cl, name, func) {
+    if (!cl.prototype[name]) {
+        Object.defineProperty(cl.prototype, name, { enumerable: false, value: func });
+    }
+};
+
+addFunc(Array, 'push8', function (num) {
     "use strict";
     this.push(num & 0xFF);
-};
+});
 
-Array.prototype.push16 = function (num) {
+addFunc(Array, 'push16', function (num) {
     "use strict";
     this.push((num >> 8) & 0xFF,
               num & 0xFF);
-};
-Array.prototype.push32 = function (num) {
+});
+
+addFunc(Array, 'push32', function (num) {
     "use strict";
     this.push((num >> 24) & 0xFF,
               (num >> 16) & 0xFF,
               (num >>  8) & 0xFF,
               num & 0xFF);
-};
+});
 
 // IE does not support map (even in IE9)
 //This prototype is provided by the Mozilla foundation and
 //is distributed under the MIT license.
 //http://www.ibiblio.org/pub/Linux/LICENSES/mit.license
-if (!Array.prototype.map) {
-    Array.prototype.map = function (fun /*, thisp*/) {
+addFunc(Array, 'map', function (fun /*, thisp*/) {
     "use strict";
     var len = this.length;
     if (typeof fun != "function") {
@@ -56,15 +62,13 @@ if (!Array.prototype.map) {
     }
 
     return res;
-    };
-}
+});
 
 // IE <9 does not support indexOf
 //This prototype is provided by the Mozilla foundation and
 //is distributed under the MIT license.
 //http://www.ibiblio.org/pub/Linux/LICENSES/mit.license
-if (!Array.prototype.indexOf) {
-    Array.prototype.indexOf = function (elt /*, from*/) {
+addFunc(Array, 'indexOf', function (elt /*, from*/) {
     "use strict";
     var len = this.length >>> 0;
 
@@ -81,8 +85,7 @@ if (!Array.prototype.indexOf) {
         }
     }
     return -1;
-    };
-}
+});
 
 // From https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys
 if (!Object.keys) {
@@ -131,8 +134,7 @@ if (!Object.keys) {
 //This prototype is provided by the Mozilla foundation and
 //is distributed under the MIT license.
 //http://www.ibiblio.org/pub/Linux/LICENSES/mit.license
-if (!Function.prototype.bind) {
-    Function.prototype.bind = function (oThis) {
+addFunc(Function, 'bind', function (oThis) {
     if (typeof this !== "function") {
         // closest thing possible to the ECMAScript 5
         // internal IsCallable function
@@ -153,8 +155,7 @@ if (!Function.prototype.bind) {
     fBound.prototype = new fNOP();
 
     return fBound;
-    };
-}
+});
 
 //
 // requestAnimationFrame shim with setTimeout fallback