tests: Delay loading old messages and starting get_updates until phantomjs thinks the page has loaded

This doesn't affect code when not in testing.  It shaves 7 seconds off of casper
test time on my machine.

(imported from commit 7e27fa781bcf16f36d9c8f058427ba57c41068bd)

static/js/util.js

@@ -345,6 +345,14 @@ if (typeof $ !== 'undefined') {
     };
 }
 
+exports.execute_early = function (func) {
+    if (page_params.test_suite) {
+        $(document).one('phantom_page_loaded', func);
+    } else {
+        $(func);
+    }
+};
+
 return exports;
 }());
 if (typeof module !== 'undefined') {