Added an if (cR < SMALL) guard to VHS sigmaTcR calculation. Giving each...

Added an if (cR < SMALL) guard to VHS sigmaTcR calculation.  Giving each processor a different random number generator seed, otherwise they follow the same sequence and are not independent.  Tnis is a practical problem because they were producing molecules with the same velocity in neighbouring cells on different procs which then collided and caused a floating point error because they had equal velocities.