Use OS based Hotkey-Modifier FS#1958

Because ALT-GR fires a CTRL-ALT event on Windows systems, but ALT-GR is
needed to write square brackets on German Keyboards, CTRL-ALT can not be
used as modifier.

This patch introdues OS dependent modifiers. Mac systems continue to use
CTRL-ALT, all other systems use only ALT.

Let's hope this works out.

lib/scripts/hotkeys.js

@@ -1,6 +1,6 @@
 /**
  * Some of these scripts were taken from TinyMCE (http://tinymce.moxiecode.com/) and were modified for DokuWiki
- * 
+ *
  * Class handles accesskeys using javascript and also provides ability
  * to register and use other hotkeys as well.
  *
@@ -17,6 +17,8 @@ function Hotkeys() {
      *  this.modifier = 'ctrl+alt+shift';
      *  this.modifier = 'alt';
      *  this.modifier = 'alt+shift';
+     *
+     *  overwritten in intitialize (see below)
      */
     this.modifier = 'ctrl+alt';
 
@@ -34,6 +36,14 @@ function Hotkeys() {
      */
     this.initialize = function() {
         var t = this;
+
+        //switch modifier key based on OS FS#1958
+        if(is_macos){
+            t.modifier = 'ctrl+alt';
+        }else{
+            t.modifier = 'alt';
+        }
+
         /**
          * Lookup all anchors with accesskey and register event - go to anchor
          * target.
@@ -97,7 +107,7 @@ function Hotkeys() {
      *
      * @param e KeyboardEvent
      * @author Marek Sacha <sachamar@fel.cvut.cz>
-     * @return b boolean 
+     * @return b boolean
      */
     this.onkeyup = function(e) {
         var t = this;