Fix typos

Allows the new_user_dialog plugin to work properly

program/lib/Roundcube/rcube_session.php

@@ -203,8 +203,8 @@ class rcube_session
             if (is_array($a_oldvars)) {
                 // remove unset keys on oldvars
                 foreach ((array)$this->unsets as $var) {
-                    if (isset($a_oldvars[$k])) {
-                        unset($a_oldvars[$k]);
+                    if (isset($a_oldvars[$var])) {
+                        unset($a_oldvars[$var]);
                     }
                     else {
                         $path = explode('.', $var);
@@ -407,7 +407,7 @@ class rcube_session
     /**
      * Unset a session variable
      *
-     * @param string Varibale name (can be a path denoting a certain node in the session array, e.g. compose.attachments.5)
+     * @param string Variable name (can be a path denoting a certain node in the session array, e.g. compose.attachments.5)
      * @return boolean True on success
      */
     public function remove($var=null)