`==` for module maps gives wrong results for non-free modules

MWE:
```
julia> M = FreeModule(ZZ, 1);

julia> N, _ = sub(M, [M([3])]);

julia> Q, _ = quo(M, N)
(Quotient module over integers with 1 generator and relations:
[3], Hom: M -> Q)

julia> f = ModuleHomomorphism(M, Q, matrix(ZZ[0;;]));

julia> g = ModuleHomomorphism(M, Q, matrix(ZZ[3;;]));

julia> map(f, gens(M)) == map(g, gens(M))  # f and g agree on all generators
true

julia> f == g
false
```