Creating a large cursor can lead to "invalid hotspot" exception on Windows

The test case attached to bug 6564923 includes a test case that attempts to
create a large cross-hair cursor. The code gets an "invalid hotspot" exception
even though the hotspot is defined to be at the center of the supplied image.

Examining the code in CustomCursor it appears that if the image is too large
then it is scaled to fit the platform's desired cursor size. Unfortunately,
the hotspot location is not modified when this happens so that a hotspot that
was formerly inside the source image may now be outside the scaled version of
the image.

If the cursor image needs to be scaled then the hotspot location should be
scaled accordingly to match the same relative location in the image.