Function: qfbnupow
Section: number_theoretical
C-Name: nupow
Prototype: GGDG
Help: qfbnupow(x,n,{L}): n-th power of primitive positive definite quadratic
 form x using nucomp and nudupl.
Doc: $n$-th power of the primitive positive definite
 binary quadratic form $x$ using \idx{Shanks}'s NUCOMP and NUDUPL algorithms;
 if set, $L$ should be equal to \kbd{sqrtnint(abs(D)>>2,4)}, where $D < 0$ is
 the discriminant of $x$.

 The current implementation is slower than the generic routine for small
 discriminant $D$, and becomes faster for $D \approx 2^{45}$.

