Add jquerycdn to blacklist

We cannot allow half-assed attempts to replace scripts that the
rest of the environment heavily depends on.

Similar functionality will be exposed via a more stable API
at some later time.

https://www.xetown.com/square/564456

common/defaults/blacklist.php

@@ -11,6 +11,7 @@ return array(
 	'errorlogger' => true,
 	'fix_mysql_utf8' => true,
 	'homepage' => true,
+	'jquerycdn' => true,
 	'member_communication' => true,
 	'multidomain' => true,
 	'seo' => true,