Fix regression in test_langs.php

Commit 78cee358 added file Web.config to plugins and lang folder.
test_langs.php treated the file as a plugin folder and a language file.
Merge branch 'fix13-test_langs' of github.com:atrol/mantisbt into atrol-fix13-test_langs
Fix #17510: regression in test_langs.php
Port bf4a7c84ec1f8c57b1cc74dacf5d17aefcf2e116 to master

This moves test icons checking functionality to a admin check
and is backported from work completed and previously in reviewed in github
from the next branch in 2011.