Needed: log1p from gnulib

[Mark H Weaver]

Hi Ludo,

I apologize for asking you again so soon, but could you possibly import
log1p from gnulib?  I'm trying to implement log for exact rationals, and
I have a serious problem with catastrophic cancellation if the numerator
and denominator are close, for example (/ big (1+ big)).  The only way
to do this even remotely well is to use log1p, which computes log(1+x)
and works well for small x, but unfortunately it's non-portable and
non-trivial to implement.

I'll have a patch ready in time for 2.0, but it will depend upon log1p.

If it's easy to import a couple more modules while you're at it, then
round and isfinite would also be useful.

   Many thanks,
      Mark