[proxy] fixing harmony/proxy.js tests and improving error messages + some drive-by fixes

src/js/v8natives.js

Index: src/js/v8natives.js
diff --git a/src/js/v8natives.js b/src/js/v8natives.js
index 1ae6e4832029b3354503b2711064290cb3fa85d0..b068ebf9094408b5449bfcd49d8026a5356ac666 100644
--- a/src/js/v8natives.js
+++ b/src/js/v8natives.js
@@ -569,7 +569,7 @@ function DefineProxyProperty(obj, p, attributes, should_throw) {
   var result = CallTrap2(handler, "defineProperty", UNDEFINED, p, attributes);
   if (!result) {
     if (should_throw) {
-      throw MakeTypeError(kProxyHandlerReturned,
+      throw MakeTypeError(kProxyTrapReturned,
                           handler, "false", "defineProperty");
     } else {
       return false;