Simplify the "smart link" behavior on drop on Desktop.

Let still move or copy files other than ones directly below home dir.
This should resemble behavior of Windows or Mac file managers.
We cannot detect "undesired" files such as http:// - GIO still tell us
those are regular files, therefore we should either hardcode http://,
https://, mms://, mailto: and similar things, or create shortcuts on
all remote URIs. Anyway, this "smart link" is optional.