Function: subgrouplist
Section: number_fields
C-Name: subgrouplist0
Prototype: GDGD0,L,
Help: subgrouplist(bnr,{bound},{flag=0}): bnr being as output by bnrinit or
 a list of cyclic components of a finite Abelian group G, outputs the list of
 subgroups of G (of index bounded by bound, if not omitted), given as HNF
 left divisors of the SNF matrix corresponding to G. If flag=0 (default) and
 bnr is as output by bnrinit, gives only the subgroups for which the modulus
 is the conductor

