bug#18638: 24.3.94; resizing of whindow by dragging the modeline does not work under xterm

[Stefan Monnier]

>> Result: At the release of the mouse button the upper window will get a
>> hight of 3 lines, irrespective of the dragging amount.
> I see this in 24.3.94 but not 24.3, so it seems to be a new issue.

Indeed, the reason is that mouse.el now uses mouse-pixel-position
instead of mouse-position in mouse-drag-line, and xt-mouse.el uses
mouse-position-function to convince mouse-position to return useful info
in xterm frames, whereas there was no such hook for
mouse-pixel-position.

I installed a patch which fixes this by making mouse-pixel-position call
mouse-position-function as well.  I think a better patch would be to
make mouse-drag-line use the event's own position info rather than calling
mouse-pixel-position, but the corresponding patch is a bit more
fiddly, so I'll keep it for after 24.4.


        Stefan