While implementing drag and drop I noticed a few glitches and bugs
* drag enter is only called after a mouse move
* drag exit is not always called
* the mouse cursor does not indicate correctly
what kind of action is associated
with the drag and drop.
* during drag and drop you can not switch the action
with the modifier keys.
At the moment I am halfway fixing these problems.
THe first two I have fixed. But this will be
quite a big patch because at the same time
I reorganized the code quite substentially.
I am not sure if this is acceptable, so
before continuing this way I would like to know
that there is a reasonable chance that
such a patch will be incorperated.