fix (again) for 0004437: Filenames of uploaded attached files are damaged
rewrote file_get_display_name to handle both old and new filename storage

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@2968 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9