Add display_default_name dwoo plugin (bug #1009777)

This just html escapes the output of display_default_name.  Existing
calls are modified to avoid double escaping.

Change-Id: I117a748a4d4cdb3313377f3441bbd20567a88fcb
Signed-off-by: Richard Mansfield <richard.mansfield@catalyst.net.nz>

htdocs/lib/dwoo/mahara/plugins/display_default_name.php

+<?php
+
+/**
+ * Dwoo {display_default_name} function plugin
+ *
+ * Type:     function<br>
+ * Date:     2012-06-11<br>
+ * Purpose:  Escape output of display_default_name for use in templates
+ * @version  1.0
+ */
+function Dwoo_Plugin_display_default_name(Dwoo $dwoo, $user) {
+    if (!$user) {
+        return '';
+    }
+
+    return hsc(display_default_name($user));
+}