Lazy mpz allocation

[Marc Glisse]

On Mon, 11 Apr 2016, Marc Glisse wrote:

> On Mon, 9 Nov 2015, Marco Bodrato wrote:
>
>> Moreover, the mpq layer and mini-gmp need to migrate to lazy allocation
>> too...
>
> For mpq, the attached seems sufficient to pass make check.

I finally pushed it. It seemed unsafe to keep mpq unaware of lazy 
allocation, in case people start swapping the numerator of a rational with 
a lazy 0 integer or something like that.

-- 
Marc Glisse