Invalid read in mpz_sub

[Torbjörn Granlund]

Vincent Lefevre <vincent at vinc17.net> writes:

  I propose the attached patch. I think that 3.4 Variable Conventions
  is the best section for such information. So, I've moved a part of
  the paragraph in 3.5 Parameter Conventions to a new paragraph in 3.4
  with more information, and I've shortened the paragraph in 3.5 to
  make it deal with only parameter conventions.

It took me some time, but no I applied your patch.
I also made some other cleanups around these sections.

Thanks for the contribution!

-- 
Torbjörn
Please encrypt, key id 0xC8601622