backing out bug 827841 patch to fix comment
Bug 827841 - don't proxy-release null pointers in nsMainThreadPtrHolder; r=jlebar
Bug 827503 - use nsMainThreadPtrHolders when passing XPCWrappedJSes around off main thread, r=bholley,jst a=blocking-basecamp+
Bug 828648 - Add system() function to JS shell, r=billm