New ECPP interface

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

Dear PARI developpers,

Karim has merged ECPP with isprime.
Now the following GP interface is provided:

isprime(N): will use best algorithm given the size of N
isprime(N,3): force use of ECPP

primecert(N): return ECPP certificate
primecert(N,1): return P-1 certificate (old isprime(P,1))

primecertexport(C):  as previous ecppexport
primecertisvalid(C): as previous ecppisvalid.

Cheers,
Bill.