Merge branch '2.0' into 2.1

diff --cc wcfsetup/install/files/lib/system/session/SessionHandler.class.php
index 47b590a249fc1bc7030c3baf8f888cbbd054e214,b15af8369367eccdb03b173506f89ccc92e572f3..e38864f87a645a9d2daa068af88919852970b1ba
--- 1/wcfsetup/install/files/lib/system/session/SessionHandler.class.php
--- 2/wcfsetup/install/files/lib/system/session/SessionHandler.class.php
+++ b/wcfsetup/install/files/lib/system/session/SessionHandler.class.php
@@@ -655,56 -478,31 +655,57 @@@ class SessionHandler extends SingletonF
         * @param       boolean                         $hideSession    if true, database won't be updated
         */
        public function changeUser(User $user, $hideSession = false) {
 -              $sessionTable = call_user_func(array($this->sessionClassName, 'getDatabaseTableName'));
 +              $eventParameters = array('user' => $user, 'hideSession' => $hideSession); 
                
 -              if ($user->userID && !$hideSession) {
 -                      // user is not a guest, delete all other sessions of this user
 -                      $sql = "DELETE FROM     ".$sessionTable."
 -                              WHERE           sessionID <> ?
 -                                              AND userID = ?";
 -                      $statement = WCF::getDB()->prepareStatement($sql);
 -                      $statement->execute(array($this->sessionID, $user->userID));
 -                      
 -                      // reset session variables
 -                      $this->variables = array();
 -                      $this->variablesChanged = true;
 -              }
 +              EventHandler::getInstance()->fireAction($this, 'beforeChangeUser', $eventParameters);
                
 -              // update user reference
 -              $this->user = $user;
 -              $this->userID = $this->user->userID ?: 0;
 +              $user = $eventParameters['user']; 
 +              $hideSession = $eventParameters['hideSession'];
                
 -              if (!$hideSession) {
 -                      // update session
 -                      $sessionEditor = new $this->sessionEditorClassName($this->session);
 -                      $sessionEditor->update(array(
 -                              'userID' => $this->user->userID
 -                      ));
 +              // skip changeUserVirtual, if session will not be persistent anyway
 +              if ($this->supportsVirtualSessions && !$hideSession) {
 +                      $this->changeUserVirtual($user);
 +              }
 +              else {
 +                      // update user reference
 +                      $this->user = $user;
++                      $this->userID = $this->user->userID ?: 0;
 +                      
 +                      if (!$hideSession) {
 +                              // update session
 +                              $sessionEditor = new $this->sessionEditorClassName($this->session);
 +                              
 +                              $this->register('__changeSessionID', true);
 +                              
 +                              try {
 +                                      $sessionEditor->update(array(
 +                                              'userID' => $user->userID
 +                                      ));
 +                              }
 +                              catch (DatabaseException $e) {
 +                                      // MySQL error 23000 = unique key
 +                                      // do not check against the message itself, some weird systems localize them
 +                                      if ($e->getCode() == 23000) {
 +                                              $sessionTable = call_user_func(array($this->sessionClassName, 'getDatabaseTableName'));
 +                                              
 +                                              // user is not a guest, delete all other sessions of this user
 +                                              $sql = "DELETE FROM     ".$sessionTable."
 +                                                      WHERE           sessionID <> ?
 +                                                                      AND userID = ?";
 +                                              $statement = WCF::getDB()->prepareStatement($sql);
 +                                              $statement->execute(array($this->sessionID, $user->userID));
 +                                              
 +                                              // update session
 +                                              $sessionEditor->update(array(
 +                                                      'userID' => $user->userID
 +                                              ));
 +                                      }
 +                                      else {
 +                                              // not our business
 +                                              throw $e;
 +                                      }
 +                              }
 +                      }
                }
                
                // reset caches