[Rd] pgeom accuracy (PR#6792)

[terra at gnome.org]

Full_Name: Morten Welinder
Version: snapshot
OS: 
Submission from: (NULL) (65.213.85.218)


This should fix the remaining two 1-p cancellation issues.

  double l_rt = log1p (-p) * (x + 1);
  if (log_p)
    return R_DT_Clog (l_rt);
  else
    return lower_tail ? -expm1 (l_rt) : exp (l_rt);