Merge revision 6500-6600 from bleeding_edge to the isolates branch.

src/date.js

Index: src/date.js
===================================================================
--- src/date.js	(revision 7030)
+++ src/date.js	(working copy)
@@ -605,7 +605,7 @@
 
 // ECMA 262 - 15.9.5.5
 function DateToLocaleString() {
-  return DateToString.call(this);
+  return %_CallFunction(this, DateToString);
 }
 
 
@@ -973,7 +973,7 @@
 // do that either.  Instead, we create a new function whose name
 // property will return toGMTString.
 function DateToGMTString() {
-  return DateToUTCString.call(this);
+  return %_CallFunction(this, DateToUTCString);
 }