experimental seadata package

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

Hello PARI-dev,

I just released the last bit of my libpari port of C. Doche and
S. Duquesne SEA.Gp implementation of the SEA algorithm for computing
the cardinal of an elliptic curve over a prime finite field.

This algorithm is accessed through the ellap() function.

This requires the experimental data package seadata.tgz, see
<http://pari.math.u-bordeaux.fr/download.html#packages>.

This implementation is sufficient to compute ellap(E,p) with
p < 2^700.

Example of use:

? allocatemem()
  *** allocatemem: Warning: new stack size = 16000000 (15.259 Mbytes).
? ellap(ellinit([0,0,0,1,17]),nextprime(2^200))
%2 = -264307979378231819420560156895
? ##
  ***   last result computed in 5,809 ms.

We are not entireley satisified with seadata.tgz, so we might need to
change it in the future, (or better, get rid of it entirely).

Cheers,
Bill.