Bug#706146: root-plugin-math-minuit2: Missing headers for Minuit2

[Peter Wienemann]

Hi Lifeng,

I am yet another person missing Minuit2 headers and therefore I would 
like to support Bastian's request. My motivation for the request 
resembles Bastian's: I am trying to build a program which contains a 
class inheriting from ROOT::Minuit2::FCNBase and Minuit2 is not the only 
ROOT dependency of the program.

Cheers, Peter