Function: rnfconductor
Section: number_fields
C-Name: rnfconductor
Prototype: GGD0,L,
Help: rnfconductor(bnf,polrel,{flag=0}): conductor of the Abelian extension
 of bnf defined by polrel. The result is [conductor,rayclassgroup,subgroup],
 where conductor is the conductor itself, rayclassgroup the structure of the
 corresponding full ray class group, and subgroup the HNF defining the norm
 group (Artin or Takagi group) on the given generators rayclassgroup[3]. If
 flag is non-zero, check that polrel indeed defines an Abelian extension

