fix spreadsheet CSP checkup and confirm that /api/broadcast is accessible

www/checkup/main.js

@@ -210,7 +210,7 @@ define([
         };
 
         $.ajax(url, {
-            success: function (data, textStatus, xhr) {
+            complete: function (xhr) {
                 cb(!Object.keys(expect).some(function (k) {
                     var response = xhr.getResponseHeader(k);
                     console.log(k, response);
@@ -220,6 +220,17 @@ define([
         });
     }, _alert("Missing HTTP headers required for XLSX export"));
 
+    assert(function (cb) {
+        cb(true);
+        $.ajax('/api/broadcast', {
+            dataType: 'text',
+            complete: function (xhr) {
+                console.log(xhr);
+                cb(xhr.status === 200);
+            },
+        });
+    }, _alert("/api/broadcast is not available"));
+
     var row = function (cells) {
         return h('tr', cells.map(function (cell) {
             return h('td', cell);