LibJS: Add ArrayPrototype and implement Array.prototype.push()

This function is ultimately supposed to be generic and allow any |this|
that has a length property, but for now it only works on our own Array
object type.

Base/home/anon/js/array.js

@@ -2,6 +2,10 @@ var a = [1, 2, 3];
 
 a[1] = 5;
 
-for (var i = 0; i < 3; ++i) {
+var push_result = a.push(7);
+
+for (var i = 0; i < a.length; ++i) {
     console.log(a[i]);
 }
+
+console.log("push result: " + push_result);