On Windows a Drag and Drop seems to be a Qt::LinkAction. And support for
symbolic links is added.

Playlist widget now uses the p_mi->dropEvent (used to have two implementation,
one calling p_mi->dropEvent already, the other had its own body. That body is
removed)

Regards,
Mario
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>