Function: polgraeffe
Section: polynomials
C-Name: polgraeffe
Prototype: G
Help: polgraeffe(f): returns the Graeffe transform g of f, such that
 g(x^2) = f(x)f(-x).
Doc: returns the \idx{Graeffe} transform $g$ of $f$, such that $g(x^2) = f(x)
 f(-x)$.
