Function: quadray
Section: number_theoretical
C-Name: quadray
Prototype: GGDGp
Help: quadray(D,f,{lambda}): relative equation for the ray class field of
 conductor f for the quadratic field of discriminant D (which can also be a
 bnf). For D < 0, lambda (if supplied) is the technical element of bnf 
 necessary for Schertz's method. In that case, return 0 if lambda is not
 suitable.

