current-time and GMP

[Stefan Monnier <monnier@IRO.UMontreal.CA>]

Of the functions that use "handmade" bignums, there's also current-time.
Since this one tends to grow over time in precision than in magnitude,
I'm wondering if people have an idea what to do with it:
- keep it as is (that's the easy way out)
- use GMP's mpf or mpq numbers (that seems like a lot of work for this
  only use, tho I guess we could then use those numbers in Calc as
  well).
- use a handmade arbitrary-precision float made up of a bignum plus
  a "scaling factor" (halfway solution: less work, but less gain).
WDYT?


        Stefan