Function Poisson-Cdf
(
poisson-cdf < k > < x > )
Computes the cumulative distribution function for a Poisson random variable
with mean `x' evaluated at `k.' The result is the probability that the number of
Poisson random events occurring will be between 0 and k-1 inclusive, if the
expected number is `x.' The argument `k' should be an integer, while `x' should
be a float. The implementation follows Numerical Recipes in C, section 6.2