Bias obtained in TH1::KolmogorovTest when using option X

The p value obtained when using TH1::KolmogorovTest with the option "X", are biased to lower values.  

The reason is that when generating pseudo-experiments only one of  the histogram is randomized. 

This affects the p-values that are displayed in the TMVAGui 

See https://root-forum.cern.ch/t/how-does-tmva-calculate-the-kolmogorov-probability/27787/15