extended fmpz_mat_snf_diagonal to cope with negative entries
extended fmpz_mat_snf_diagonal to cope with negative entries

dsroche/flint2,fredrik-johansson/flint2,jpflori/flint2,wbhart/flint2,fredrik-johansson/flint2,jpflori/flint2,jpflori/flint2,dsroche/flint2,jpflori/flint2,fredrik-johansson/flint2,dsroche/flint2,dsroche/flint2,wbhart/flint2,wbhart/flint2