[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 7e62dadb051e1b7d9c7628222068974c5067c1a2..19c2ff6df0669fb00b3c2ce1e00bffb29ca4daee 100644
--- a/src/js/v8natives.js
+++ b/src/js/v8natives.js
@@ -568,7 +568,7 @@ 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;