1. Fixed a problem where users below the threshold to view private bugnotes
   were not able to view any bugnotes.
2. Fixed a problem where the number of bug notes in the view bugs page
   were reflecting all bug notes rather than only the ones that the logged in user
   can view.
3. Removed calls to check_bug_exist() from the code in view_bug_page
   and view_bug_advanced_page and added the check in the code since the
   same query was being executed twice, once to check and once to retrieve
   the data.
4. Added DISTINCT when retrieving the language in core_API. We should
   do that in all queries that are expecting one row. Hence, mySQL will not have
   to search the whole table, but will search till it finds the first one.

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1103 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9