Convexity returns true for carefully constructed non-convex polycones

Inspection of new method CheckContinuityInSlopes() suggested that polycones with zPlane[j]==zPlane[j+1] could exit out of a loop and immediately return true. A carefully constructed non-convex polycone was used to demonstrate the problem:

    int nZ = 5;

    double rmin[5] = {0.,0.,0.,0.,0.};

    //double rmax[5] = {5.,10.,10.,20.,20.};   // bad

    double rmax[5] = {15.,20.,20.,10.,5.};   // bad

    double z[5]    = {0.,10.,20.,20.,40.};

This problem was originally reported by Philippe Canal.