Off-by-one rounding issue causes $img2 to shift by 1px when manipulating crop box

When manipulating cropbox, moveTo method is passed x and y values from Coords.getFixed. These numbers are quite oftentimes decimal values. When the decimal value is a non-integer multiple of 0.5 (1.5, 2.5, 99.5, 102.5), the rounding resulting in the left and top offsets is off-by-one. This is because the number is first made negative and THEN the rounding occurs, e.g.:

Math.round(0.5); // === 1
Math.round(-0.5); // === 0;

The solution might be to patch the "px" method - but it's used in so many places that I was unwilling to simply cowboy a patch and hope for the best.

![Jcrop-off-by-one](https://f.cloud.github.com/assets/884507/58429/7b10770c-5b70-11e2-813e-4e4c30b7c6fe.png)