New GP functions qfauto/qfisom etc.

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

Dear developers,

I just commit a patch that add a number of PARI functions for
automorphisms and isomorphisms of lattices

This is a port of the program ISOM by Bernt Souvignier which implement an
algorithm published in
W. PLESKEN, B. SOUVIGNIER, Computing Isometries of Lattices,
Journal of Symbolic Computation, Volume 24, Issues 3-4, September 1997,
Pages 327-334, ISSN 0747-7171, 10.1006/jsco.1996.0130.
(http://www.sciencedirect.com/science/article/pii/S0747717196901303)

I like to thanks Prof. Souvignier for his permission to use his code in PARI/GP.

The new functions are
qfauto(L): computes the automorphisms of the lattice L given by its Gram matrice.
qfisom(L1,L2): compute an isorphimsm between L1 and L2.
qfisominit(L1): precompute data for faster computation of isomorphisms with L1
qfautoexport(): export the output of qfauto to GAP or MAGMA format (as a matrix
group).

This port is dedicated to Philippe Elbaz-Vincent. Enjoy it!

Please test!

Cheers,
Bill.