#1 DnD across two FSB instances doesn't work properly

[wernerfragner]

When having two instances of FileSystemBrowser
(ExampleFSB) then following bugs occur when dragging
and dropping among these two instances:
- DnD from second instance to first instance: target and
source are being exchanged first instance is being
refreshed, the second one not
- DnD from first instance to second instance: DnD has no
effect (does nothing)
- DnD with a DriveNode as target: DnD has no effect
(does nothing)