new GP language feature: simultaneous affectations

[Bill Allombert <Bill.Allombert@math.u-bordeaux1.fr>]

Dear PARI developpers,

I have created a GIT branch 'bill-multi_affect'
which allow to affect several values at once:

? [a,b,c]=[1..5]
%1 = [1,2,3,4,5]
? [a,b,c]
%2 = [1,2,3]
? [a,b]=[b,a]
%3 = [2,1]
? [a,b,c]=[1..2]
  ***   at top-level: [a,b,c]=[1..2]
  ***                      ^---------
  ***   array index (3) out of allowed range [1-2].

Currently, affecting to components (a[i] etc.) is not supported.

Please check it.

Cheers,
Bill.