SEA without seadata

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

Dear PARI developers,

I have pushed a patch to master which allow ellap/ellcard to use the
function polmodular written by Hamish instead of (or in addition to) 
the seadata database for the SEA algorithm.

This means that you can now:

1) use SEA without installing seadata (but this is will be at least three time
slower)

2) use SEA for fields that are so large they exhaust seadata. 

Cheers,
Bill.