Make instanceof and Object.getPrototypeOf work for proxies, plus a few other tweaks.

src/proxy.js

Index: src/proxy.js
diff --git a/src/proxy.js b/src/proxy.js
index d90e5d4ca8ad50f9a2793a74fc20cb4d2ceb5130..cb9c020e35c60c9b0cdcf15e961ca9a8fdb73789 100644
--- a/src/proxy.js
+++ b/src/proxy.js
@@ -60,8 +60,9 @@ $Proxy.createFunction = function(handler, callTrap, constructTrap) {
 }
 
 $Proxy.create = function(handler, proto) {
-  if (!IS_SPEC_OBJECT(handler)) throw TypeError
-  if (!IS_SPEC_OBJECT(proto)) proto = $Object.prototype
+  if (!IS_SPEC_OBJECT(handler))
+    throw MakeTypeError("handler_non_object", ["create"])
+  if (!IS_SPEC_OBJECT(proto)) proto = null  // Mozilla does this...
   return %CreateJSProxy(handler, proto)
 }
 
@@ -130,3 +131,7 @@ function DerivedSetTrap(receiver, name, val) {
     configurable: true});
   return true;
 }
+
+function DerivedHasTrap(name) {
+  return !!this.getPropertyDescriptor(name)
+}