Function: galoisisabelian
Section: number_fields
C-Name: galoisisabelian
Prototype: GD0,L,
Help: galoisisabelian(gal,{flag=0}): gal being as output by galoisinit,
 return 0 if gal is not abelian, the HNF matrix of gal over gal.gen if
 flag=0, 1 if flag is 1, and the SNF of gal is flag=2

