[css3-ui] out-of-range <x>,<y> of 'cursor'

9.1.1. ‘cursor’ property

I think the spec needs to say what should happen if <x>, <y> isn't in
the image (say, one of them is less than zero or greater than the size
of the image). Upon testing Firefox 10 and Chromium 18, these are
floored from the image boundary.

Cheers,
Kenny