this patch fixes issues that limited the scope of Drag&Drop.
- set the version number to the latest one (version 5 in 2003!)
- ensure the data type is not hardcoded but selected at runtime.
- add a XSync to ascertain full completion of Drag and Drop.
- protect against possible overflow
- add some debugging info

(cherry picked from commit c5213920

)
Signed-off-by: Erwan Tulou <erwan10@videolan.org>