Function: nfisincl
Section: number_fields
C-Name: nfisincl
Prototype: GG
Help: nfisincl(x,y): tests whether the number field x is isomorphic to a
 subfield of y (where x and y are either polynomials or number fields as
 output by nfinit). Return 0 if not, and otherwise all the isomorphisms. If y
 is a number field, a faster algorithm is used

