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
Following merge of #216 - update calls to db_get_table().

#216 adds support for the new table name syntax,
allowing us to replace db_get_table calls within queries.

Calls to db_get_table that are used by other database function,
i.e. db_insert_id, db_field_exists are deliberately left unchanged at this
stage.

This is aimed at breaking down the future DB API changes into manageable
chunks, and to aid the review process after 1.3 for 2.0.

This Pull request deals with calls for the 'plugin' table only,
for ease of review, and syncing until merged.