Added conway polynomial retrieval from flint.

This version requires flint to be enabled.  Moved around some
defs, adding util.{hop,cpp}.  Changed how to get coefficients
from a (univariate) polynomial.
Refactoring minimal poly code for GF, part 1.

Functionality hasn't changed yet (i.e. only original GF code works
with factorization of polynomials over that field).
Refactoring GF factorization, part 2.

factorization in poly rings over GF (original, new, givaro) are functional.