bug#16594: 24.3.50; very slow redraw when resizing windows horizontally

[martin rudalics]

> I see it now.  I just had assumed that window-resize-pixelwise was
> already t by default (this assumption was based on the behavior while
> dragging windows ;-).

Apart from frame maximizing, line dragging should be the only occasion
where pixelwise resizing leaks through by default.  I forgot to change
mouse.el appropriately, maybe so because it wasn't too trivial.

> I think the default for that should be t.  But we can delay this change
> to post-24.4.

OK.

martin