M config_defaults_inc.php

• Added "history_default_visible" config. When ON the bug history is displayed
  by default.

M bug_view_advanced_page.php
M bug_view_page.php

• Modified both pages to use the new config.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1836 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9