BoxIntegral gives negative values about libmv HOT 2 CLOSED

After some investigation, I see that the problem is floating point precision. 
The box
integral code triggers catastrophic cancellation. The proper solution is to 
switch to
using either int32's (max image size would be ~4k x 4k) or int64's for the 
integral
image.

I'm working on a fix.

I switched to use an integer matrix for the integral image. Unfortunately SURF
doesn't seem to work reliably.