* fixed drag & drop issue in column view (dropping on files was not possible -> handl...

* fixed drag & drop issue in column view (dropping on files was not possible -> handled as viewport now)
* only show the hover-drop-indicator on directories (dropping on file-items is handled like dropping on the viewport)
* simplified signature of drop signal (source widget not required anymore)

svn path=/trunk/KDE/kdebase/apps/; revision=731129