bug#19988: 25.0.50; Drag events ending in different frame

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

> How do we include both in a backward-compatible way?

Good question.  Maybe we can return only one of the two and find a way
to implement a function that computes the other from the one
that's returned.

> When I select a region by dragging Mouse-1 starting at the "selected."
> above, as soon as the mouse cursor leaves the emacs frame, the region
> won't grow or shrink anymore until I enter the frame and window again.

Indeed, sorry.  Dragging keeps working when you drag a mode-line but not
when you drag a region.  Not sure why.  Looks like a bug to me.

Actually, it's more subtle than that: if I move into another frame which
hides part of the selected window, the drag keeps working (as long as
I stay within the bounds of the originally selected window, even though
I don't get to see some of those bounds because they're hidden by
another frame).

Oh, and there's yet another subtlety: if, during the drag, you move the
mouse out of the selected frame, the drag seems to freeze indeed, but if
you then move your mouse higher/lower than the frame the text gets
scrolled and the drag does take place (even if you release the mouse
while it's outside of the originally selected frame/window).


        Stefan