The operator `operator/(Mpfz,Mpfz)` actually implements integral
division. With this commit, it is renamed `division((Mpfz,Mpfz)`
unless the macro `CGAL_MPZF_DIVISION_OPERATOR` is defined.
I have commented the line
#define CGAL_MPZF_DIVISION_OPERATOR 1
and that will breaks a lot of CGAL code in this branch.