fix for 0004932: In advanced filter mode, display 'empty' values in drop-down lists as '[empty]'
instead showing blank list box entry
fix for 0004718: Not possible to select blank fields in filter
partial fix for 0005075: Add additional standard filter attributes
Note: filters need to be refreshed

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@3232 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9