Cleanups

[Torbjorn Granlund]

I did a lot of cleanup changes today:

1. All LGPL copyright headers should now have the same layout, except
   for file format mandated line prefixes.

2. Old K&R varargs config checks and conditional code is now gone.

3. mpq_t now used everywhere in place of the old MP_RAT.

4. The old BITS_PER_MP_LIMB is no more.

After discussion with Niels, I renamed mpn_sec_minvert to mpn_sec_invert
in analogy to the public mpz_invert.  We have a non-public mpn_invert
function family, which actually computes a fraction.  I suggest that we
rename them to something like mpn_finvert* (at least before they are
made public).


Torbjörn