nice undocumented feature

[Max Alekseyev <maxale@gmail.com>]

I've just noticed that divisors(X), fordiv(X,...), sumdiv(X,...)
functions accept as an argument the factorization of X instead of X,
e.g.:

? divisors([3,1;5,1])
%1 = [1, 3, 5, 15]

I found this feature very helpful (for X with known but hard to
compute factorizations) and deserving to be documented.

Regards,
Max