Calculate distance between two points

The calculation of distance between two points using standard spherical geometry can be inaccurate for short distances (ten miles or less) because the sine function of very small angles approaches zero. The haversine approach (http://en.wikipedia.org/wiki/Haversine_formula) turns this around, so it is very accurate at small distances but has larger errors (about ten miles) for points on opposite sides of the earth.

I thought this function was a great candidate for conversion to CLR, but it was actually a little slower on my test system. My theory is that the cost of marshalling the arguments outweighs any benefit of running compiled code for this function.