mpn_cnd_add_n

[Torbjorn Granlund]

  Here's a patch that reorders the arguments for mpn_addcnd_n and
  mpn_subcnd_n (I think it's best to keep this change separate from the
  renaming, since the potential problems are quite different).

  It's tested on x86_64, arm, and with --disable-assembly. I've run a
  regular make check and tests/devel/try, and tune/speed. I haven't tested
  the (apparently trivial) powerpc64 change.

The powerpc64 change could be tested on g5.gmplib.org (where you should
have an account).

  I you think this is ok, I'll check it in, and look into the renaming
  next.

OK with me, but either test on powerpc64 before checking in, or keep an
eye on nightbuild regressions and fix any problem there.

-- 
Torbjörn