Function: qfbpow
Section: number_theoretical
C-Name: qfbpow
Prototype: GG
Help: qfbpow(x,n): n-th power with reduction of the binary quadratic
 form x.
Doc: $n$-th power of the binary quadratic form
 $x$, computed with \idx{reduction} (i.e.~using \kbd{qfbcomp}).
