parallel bnfinit

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

Dear PARI developers,

With Loïc Grenié, we have experimented with a parallel version
of bnfinit (the git branch bill-bnfinit-parallel).

I managed to compute bnfinit(x^97-x-1) in 7h, 16min on 128 cores.
(518h, 21min of total time).
The regulator is 2.422012163387226001 e57

Cheers,
Bill