Changes related to enhancement 0002377: index user names in manage user page by letters.
(some config_defaults_inc.php cleanup included as well)

M config_defaults_inc.php

• Added $g_default_manage_user_prefix with default value 'ALL'
• Some cleanup
• Use domain example.com rather than nowhere / yourhostnamehere.

M manage_user_page.php

• Default the user prefix to $g_default_manage_user_prefix.
• Use language string show_all_users rather than hard-coded value 'ALL'.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2210 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9