More tests.
I think we have all the functions and tests now.
This commit most probably will not compile for Graph_functions2, but
I'd rather not take a chance when I am changing code at such a rapid
pace.
OK, we have a clean compile for Graph_functions2.ml. Onwards!
Right now, our code compiles, but throws this weird error which arises
from Ocaml not being able to compute equality on (or, in general,
compare) two different values of the type raw_t because they are
"abstract" (that is, the underlying data is not visible to Ocaml.). We
need to fix this by implementing our own equality types.