Function: ellintegralmodel
Section: elliptic_curves
C-Name: ellintegralmodel
Prototype: GD&
Help: ellintegralmodel(E,{&v}): given an elliptic curve E defined
 over a number field, returns an integral model. If v is present,
 sets the variable v to the corresponding change of variable.
Doc: Let $E$ be an \kbd{ell} structure over a number field $K$. This function
 returns an integral model. If $v$ is present, sets $v = [u,0,0,0]$ to the
 corresponding change of variable: the return value is identical to that of
 \kbd{ellchangecurve(E, v)}.
