stricter tests for the sandbox checkup

www/checkup/main.js

@@ -42,12 +42,13 @@ define([
         return void cb(trimmedSafe !== trimmedUnsafe);
     }, _alert('Sandbox configuration: httpUnsafeOrigin !== httpSafeOrigin'));
 
+    assert(function (cb) {
+        cb(trimmedSafe === ApiConfig.httpSafeOrigin);
+    }, "httpSafeOrigin must not have a trailing slash");
+
     assert(function (cb) {
         var origin = window.location.origin;
-        return void cb([
-            origin,
-            origin + '/'
-        ].indexOf(ApiConfig.httpUnsafeOrigin) !== -1);
+        return void cb(ApiConfig.httpUnsafeOrigin === origin);
     }, _alert('Sandbox configuration: loading via httpUnsafeOrigin'));