Merge branch '2.1' into 3.0

diff --cc wcfsetup/install/files/lib/acp/form/UserGroupAddForm.class.php
index 591d3a504feb082055a42835a3e9c27d4f13e56f,bbe09de46fa711b640257d373663c9881ec186b9..05bfd5489fc6a7c55c5327a0a5d894032f1298a6
--- 1/wcfsetup/install/files/lib/acp/form/UserGroupAddForm.class.php
--- 2/wcfsetup/install/files/lib/acp/form/UserGroupAddForm.class.php
+++ b/wcfsetup/install/files/lib/acp/form/UserGroupAddForm.class.php
@@@ -185,6 -188,8 +185,7 @@@ class UserGroupAddForm extends Abstract
                
                // reset values
                $this->groupName = '';
 -              $this->optionValues = array();
+               $this->priority = 0;
                
                I18nHandler::getInstance()->reset();
        }