numbers.h: two more things

[Michael Livshin]

* the function scm_2ulong2big is not used anywhere in Guile.  it seems
  extremely esoteric, I had to read the source to understand what it
  does, and after I understood what it does I don't think anybody
  needs it (it makes a bignum out of 2 unsigned longs.  why 2 and not
  `n'?  why both unsigned?).

  deprecate?

* the function scm_dbl2big should be made internal.  a new function
  called scm_dbl2num should be introduced instead.

  deprecate?

-- 
All ITS machines now have hardware for a new machine instruction --
BOT
Branch On Tree.
Please update your programs.