added generating function EmpiricalDistribution which provide a simple wrapper to function DiscreteDistribution

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/distr@960 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added generating function EmpiricalMVDistribution as a simple wrapper to DiscreteMVDistribution. 
In addition, removed definition of PI as it is already defined in the included R.h. 
Futhermore, distrEx now depends on R >= 2.10.0.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/distr@961 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
updated NEWS file

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/distr@962 edb9625f-4e0d-4859-8d74-9fd3b1da38cb