BUG: Fixed bug in vtkAMRBox and added better error checking.

The Intersect function was not taking the last cells into account when doing intersection checking. This is incorrect because the high HiCorner of a vtkAMRBox in inclusive - those cells are actually in the data. I fixed this. Also fixed how the intersection was decided - if both boxes are empty in a particular dimension, they should still be counted as intersecting. This is essential for 2D boxes. I also added better error checking during parent-child calculation. The assumption is that at the time we are checking intersection between the parent and its children, we already know that there is intersection. Otherwise, there is a bug.