Parameterized list of admin users.  The list is set in config.php as

$yourls_multiuser_admin_users = array('admin','foo',...);

The users can be either local or LDAP users.
- replace deprecated yourls call yourls_plural with yourls_n
- fixed syntax errors in mufunctions
- fixed error isAdmin function
- possibly a problem with submiting URLs to shorten for non admins