Enh 0003903: optimisation of lang_load_default()

M core/lang_api.php

• (lang_load_default): Re-implemented to achieve the following:
  • Avoid using cookies directly, use auth_api.php instead.
  • Use user_pref_api.php rather than a direct query. Makes use of caching as well.
  • Simpler implementation.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2593 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9