_fq_reduce, _fq_sparse_reduce, _fq_dense_reduce

Reduce the polynomial (R, lenR), with arbitrary integer coefficients and \mathit{lenR} \le 2d (any length for _fq_sparse_reduce), modulo p and modulo the defining polynomial f in place: the first \min(\mathit{lenR}, d) coefficients receive the reduced value (and are not normalised). _fq_sparse_reduce eliminates the coefficients of degree at least d from the top, using the nonzero terms of the monic version of f, and reduces modulo p at the end; it costs about (\mathit{lenR} - d) \cdot t multiplications for f with t nonzero terms. _fq_dense_reduce reduces modulo p and then divides by f with the precomputed inverse (Newton division, _fmpz_mod_poly_divrem_newton_n_preinv). _fq_reduce calls the first if f has at most five nonzero terms and the second otherwise.