[polyselect2l] combine the computation of (rp-rq)/q^2
[polyselect2l] combine the computation of (rp-rq)/q^2

mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs,mancoast/cado-nfs