Made EmpiricalDistribution smoothing kernel pluggable.
To enable subclasses to provide the enclosing distribution's underlying RandomGenerator
to distribution constructors, two more changes were required:
* In EmpiricalDistribution, the RandomDataGenerator field (randomData) was changed
  from private to protected.
* The private getRan() method in RandomDataGenerator returning the underlying
  RandomGenerator was renamed getRandomGenerator and made public.
JIRA: MATH-671

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/math/trunk@1457372 13f79535-47bb-0310-9956-ffa450edef68