Modified KolmogorovSmirnovTest cdf computation to use the Pelz-Good
approximation (per Simard-L'Ecuyer) for n > 140.  Removed R reference tests, as
our implementation is now different (but should be more accurate)
for the n values covered by the tests.
Also added a PI_SQUARED constant to MathUtils.
JIRA: MATH-1131



git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1613723 13f79535-47bb-0310-9956-ffa450edef68