bug#16647: Imprecisions with window-resizing cursors

[martin rudalics]

I now tried to address the following issues reported here:

> On GTK3 with Emacs built from trunk on 2014-02-10, I do not see the
> symptoms above exactly, but I do see another bug.
>
> With the recipe above:
>
> lag in appearance of <=> handle (probably okay?)
> ================================================
> As the mouse cursor crosses the vertical line there _is_ a distinct lag
> in the appearance of the <=> handle, so that it _does_ appear to the
> left or right of the line (depending upon which direction the mouse was
> moving), unless the mouse movement is _extremely_ slow. I don't think
> this behaviour is particularly unusual (although it seems part of a
> distinct sluggishness in the windowing interface that wasn't there in
> Emacs 24.3.1). The <=> handle never first appears further from the
> vertical line than (roughly?) the width of the fringe. That is, the <=>
> handle doesn't appear at all if one moves the mouse over the vertical
> line too quickly, and this seems okay too.

I'm not all to sure about this.  But with a right fringe larger than the
default character width it was possible to not show the <=> until the
mouse was right over the vertical border.  This should be fixed now.
Please try again.

> Another bug
> ===========
> When the vertical line is as far to the right in the frame as it will go
> (i.e., when the right window is as narrow as permitted), then the <=>
> handle only appears when the mouse cursor approaches the vertical line
> from the right. If the mouse cursor approaches the vertical line from
> the left, the <=> handle fails to appear. (Ditto with "left" and "right"
> reversed in that statement.)

This might be due to the same reason as the issue described above.  The
mouse cursor won't appear when approaching the border from the left.
Please try again.

martin