Fix bugs in Base.in methods and empty comprehension

[samuelsonric]

• The in functions were not really causing problems, since Julia was defaulting to iterating over the container. However, it was creating method ambiguities (I caught it with Aqua).
• In the function make_homomorphism the comprehension [row[i+=1] for _ in parts(X,c)] is creating a vector of type Any if parts(X, c) is empty.

[epatters]

Thanks Richard! I don't know how we got all those Base.in methods backward.