add method DistSampler::Init passing the options

 add new class TFoamSampler implementing the DistSampler interface using TFoam

 fix correct number of function calls when using the Fumili-like methods


git-svn-id: http://root.cern.ch/svn/root/trunk@37232 27541ba8-7e3a-0410-8455-c3a389f83636