Function: rnfisnorminit
Section: number_fields
C-Name: rnfisnorminit
Prototype: GGD2,L,
Help: rnfisnorminit(pol,polrel,{flag=2}): let K be defined by a root of pol,
 L/K the extension defined by polrel. Compute technical data needed by
 rnfisnorm to solve norm equations Nx = a, for x in L, and a in K. If flag=0,
 do not care whether L/K is Galois or not; if flag = 1, assume L/K is Galois;
 if flag = 2, determine whether L/K is Galois.
Doc: let $K$ be defined by a root of \var{pol}, and $L/K$ the extension defined
 by the polynomial \var{polrel}. As usual, \var{pol} can in fact be an \var{nf},
 or \var{bnf}, etc; if \var{pol} has degree $1$ (the base field is $\Q$),
 polrel is also allowed to be an \var{nf}, etc. Computes technical data needed
 by \tet{rnfisnorm} to solve norm equations $Nx = a$, for $x$ in $L$, and $a$
 in $K$.

 If $\fl = 0$, do not care whether $L/K$ is Galois or not.

 If $\fl = 1$, $L/K$ is assumed to be Galois (unchecked), which speeds up
 \tet{rnfisnorm}.

 If $\fl = 2$, let the routine determine whether $L/K$ is Galois.
