Revision 140848

Commited patch for issue 20112 from Phil Steitz.

EmpiricalDistribution -- represents an empirical probability distribution and
supports generation of data values that are "like" values in an input file
without making any assumptions about the functional form of the probability
distribution that the data come from.   This is useful in simulation
applications where historical data about component performance are
available but do not follow standard distributions (or any application that
requires random data generation from an empirical distribution). Also
generates data for grouped frequency histograms based on the input file.

ValueServer -- a wrapper for RandomData and EmpiricalDistribution that
generates values in each of the following modes:
  * DIGEST_MODE -- uses an empirical distribution
  * REPLAY_MODE -- replays data from an input file
  * UNIFORM_MODE -- generates uniformly distributed random values
  * EXPONENTIAL_MODE -- generates exponentially distributed random
                        values
  * GAUSSIAN_MODE -- generates Gaussian distributed random values
  * CONSTANT_MODE -- returns the same value every time.