Function: polisirreducible
Section: polynomials
C-Name: isirreducible
Prototype: lG
Help: polisirreducible(pol): true(1) if pol is an irreducible non-constant
 polynomial, false(0) if pol is reducible or constant.
Doc: \var{pol} being a polynomial (univariate in the present version \vers),
 returns 1 if \var{pol} is non-constant and irreducible, 0 otherwise.
 Irreducibility is checked over the smallest base field over which \var{pol}
 seems to be defined.
