[cairo] Pixman sampling coordinates

[Bill Spitzak]

Carl Worth wrote:

> rotate-image-surface-paint is passing in the no-offset case while
> failing in the case of a 25x25 offset.
> 
> Something's really fishy there, because an integer offset should not
> be changing the sampling behavior.
> 
> So, chalk another point up for the test suite. But, Bertram, what did
> we miss in the image sampling code?

Could this be rint rounding x.5 to the nearest *even* number. Ie if x is 
odd it rounds up, but if x is even it rounds down.