Function: qfrep
Section: linear_algebra
C-Name: qfrep0
Prototype: GGD0,L,
Help: qfrep(q,B,{flag=0}): vector of (half) the number of vectors of norms
 from 1 to B for the integral and definite quadratic form q. Binary digits of
 flag mean 1: count vectors of even norm from 1 to 2B, 2: return a t_VECSMALL
 instead of a t_VEC.
Doc:
 $q$ being a square and symmetric
 matrix with integer entries representing a positive definite quadratic form,
 outputs the vector whose $i$-th entry, $1 \leq i \leq B$ is half the number
 of vectors $v$ such that $q(v) = i$. This routine uses a naive algorithm
 based on \tet{qfminim}, and will fail if any entry becomes larger than
 $2^{31}$.

 \noindent The binary digits of \fl\ mean:

 \item 1: count vectors of even norm from $1$ to $2B$.

 \item 2: return a \typ{VECSMALL} instead of a \typ{VEC}
