hopefully fix db_field_exists for multiple database support.
Also remove unused 'database name' param from db_field_exists
Fix: db_pconnect function

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2633 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9