Function: fffrobenius
Section: number_theoretical
C-Name: fffrobenius
Prototype: GD1,L,
Help: fffrobenius(m,{n=1}): return the n-th power of the Frobenius map over
 the field of definition of m.
Doc: return the $n$-th power of the Frobenius map over the field of definition
 of $m$.
 \bprog
 ? a = ffgen([3,5],'a);
 ? f = fffrobenius(a);
 ? ffmap(f,a) == a^3
 %3 = 1
 ? g = fffrobenius(a, 5);
 ? ffmap(g,a) == a
 %5 = 1
 ? h = fffrobenius(a, 2);
 ? h == ffcompomap(f,f)
 %7 = 1
 @eprog
