Fix of memory leak in Function.prototype.bind function.

Related issue: #511

JerryScript-DCO-1.0-Signed-off-by: Zsolt Borbély zsborbely.u-szeged@partner.samsung.com

tests/jerry/function-prototype-bind.js

@@ -115,6 +115,9 @@ assert (foo == 3);
 assert (foo instanceof Number);
 assert (foo.prototype === undefined);
 
+var func = Number.prototype.toString.bind('foo');
+assert (func instanceof Function);
+
 try {
   var this_obj = this.constructor;
   var bound = this_obj.bind(null, "foo");