Modify fmpz_poly_signature to match Cohen's algorithm 4.1.11
Modify fmpz_poly_signature to match Cohen's algorithm 4.1.11

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