- use std::string for parameter name and remove un-necessary limitation on the length of parameter name
   maintan the Name() method returning a char * (for backward compatibility) and add a new method GetName() returning 
   a reference to a std::string
- add also a method in MInuit2Minimizer to get correlation coefficient between parameter i and j  and a method to get 
  the global Correlation coefficient of parameter i
- add new complex tests of fitting used for parallelization studies 
- compile in ROOT also the tests in MnSim and MnTutorial


git-svn-id: http://root.cern.ch/svn/root/trunk@24400 27541ba8-7e3a-0410-8455-c3a389f83636