add stack trace to the crawler's errorHandler

lib/crawler.js

@@ -131,7 +131,7 @@ class Crawler {
       if (requestBox[0].processControl === 'requeue') {
         return requestBox[0];
       }
-      return requestBox[0].markDead('Error', error.message);
+      return requestBox[0].markDead('Error', `${error.message}\n\n${error.stack}`);
     }
     // otherwise, it is early in the processing loop so no request yet.  Make up a fake one
     // so we can complete the processing loop