Global no longer uses root as alt object prototype

This is a bugfix; the bug was introduced in v0.2.3.

Initially, the implementation created a new object with the root object as
its prototype, taking advantage of ECMAScript's native
overrides/fallthroughs. Unfortunately, IE<=8 had a buggy implementation,
effectively treating the prototype as an empty object. So, rather than
alt.Array === root.Array, alt.Array === undefined.

The fix is simply to reference discrete objects.

lib/util/Global.js

@@ -45,9 +45,11 @@ function Global()
         return new Global();
     }
 
-    // allows us to extend the global object without actually polluting the
-    // global scope
-    this._global = new _G();
+    // do not pollute the global scope (previously, _the_global was used as
+    // the prototype for a new object to take advantage of native overrides,
+    // but unfortunately IE<=8 did not support this and always returned
+    // undefined values from the prototype).
+    this._alt = {};
 }
 
 
@@ -56,8 +58,9 @@ function Global()
  * versions, for any root variable name, and works with ES5 strict mode.
  *
  * As an example, Node.js exposes the variable `root` to represent global
- * scope, but browsers expose `window`. Further, ES5 strict mode will provde
- * an error when checking whether `typeof SomeGlobalVar === 'undefined'`.
+ * scope, but browsers expose `window`. Further, ES5 strict mode will
+ * provide an error when checking whether `typeof SomeGlobalVar ===
+ * 'undefined'`.
  *
  * @return  {Object}  global object
  */
@@ -86,12 +89,14 @@ Global.prototype = {
      */
     provideAlt: function( name, f )
     {
-        if ( typeof this._global[ name ] !== 'undefined' )
+        if ( ( _the_global[ name ] !== undefined )
+            || ( this._alt[ name ] !== undefined )
+        )
         {
             return;
         }
 
-        this._global[ name ] = f();
+        this._alt[ name ] = f();
         return this;
     },
 
@@ -112,7 +117,9 @@ Global.prototype = {
      */
     get: function( name )
     {
-        return this._global[ name ];
+        return ( this._alt[ name ] !== undefined )
+            ? this._alt[ name ]
+            : _the_global[ name ];
     },
 };