MDL-11295 editorshortcutshelpbutton breaking xhtml strict

lib/weblib.php

@@ -4327,8 +4327,11 @@ function print_textarea($usehtmleditor, $rows, $cols, $width, $height, $name, $v
 
     if ($usehtmleditor) {
         // Show shortcuts button if HTML editor is in use, but only if JavaScript is enabled (MDL-9556)
-        $str .= '<script type="text/javascript">document.write(\''.
-            str_replace('\'','\\\'',editorshortcutshelpbutton()).'\'); </script>';
+        $str .= '<script type="text/javascript">
+//<![CDATA[
+document.write(\''.addslashes_js(editorshortcutshelpbutton()).'\');
+//]]>
+</script>';
     }
 
     if ($return) {