Lone categories when no parent can be assigned get same inputLabel (and hence callback) as parentable categories. New l10n string (category_parent) required though. Fixes Issue 370. Thanks ph.wittenbergh

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5496 2fea6a4d-a838-0410-917b-93a53c48e9d2