Bug#838324: xfdesktop4: drag and drop copies

[Akbarkhon Variskhanov]

Control: tags -1 moreinfo upstream

Related upstream bugs (depending on whether you have Thunar or other
file managers):
https://bugzilla.xfce.org/show_bug.cgi?id=2644
https://bugzilla.xfce.org/show_bug.cgi?id=13929