Make Function.prototype a function

Issue #561

Author: marijnh

lib/infer.js

@@ -735,7 +735,8 @@
       cx.topScope = new Scope();
       cx.topScope.name = "<top>";
       cx.protos.Array = new Obj(true, "Array.prototype");
-      cx.protos.Function = new Obj(true, "Function.prototype");
+      cx.protos.Function = new Fn("Function.prototype", ANull, [], [], ANull);
+      cx.protos.Function.proto = cx.protos.Object;
       cx.protos.RegExp = new Obj(true, "RegExp.prototype");
       cx.protos.String = new Obj(true, "String.prototype");
       cx.protos.Number = new Obj(true, "Number.prototype");