reload: Catch exceptions aborting pending AJAX requests.

It's probably a bug that this throws exceptions sometimes, but it's
not consistently reproducible (or maybe, browser dependent?), and it
isn't really a problem to fail to abort some requests as part of the
page reload process; the abort was just there to make sure as little
as possible is happening so we can garbage-collect effectively.

static/js/reload.js

@@ -145,7 +145,12 @@ function cleanup_before_reload() {
         $('*').off();
 
         // Abort all pending ajax requests`
+        try {
             channel.abort_all();
+        } catch (ex) {
+            // This seems to throw exceptions for no apparent reason sometimes
+            blueslip.debug("Error aborting XHR requests on reload; ignoring");
+        }
 
         // Free all the DOM in the main_div
         $("#main_div").empty();