Add possibility to permute variable for a specific kpca axe.
kernel.pca.permute allows to compute the Crone and Crosby distances by permuting variables on multiple axes. The number of axes is given by the parameter ncomp. Change the parameter to allow to perform the permutation on a specific axe. Example, ncomp=c(1,3) on the 3 first axes, ncomp=2 only on the second one.