Back out pull request 6150, which is incompatible with ROOT6

This is a semi-urgent request to revert or back out pull request 6150, which is incompatible with ROOT6, and breaks the build.

TFitterMinuit is an obsoleted interface in ROOT 6. To minimize a 
function using Minuit2, one should use the ROOT::Math::Minimizer 
interface or directly ROOT::Minuit2::Minuit2Minimizer
see 
http://root.cern.ch/drupal/content/numerical-minimization#multidim_minim
The ROOT6 IB is dead until this is merged or 6150 is reverted (should be equivalent).