Graphs with custom eq/hash don't seem to use them

[aphyr]

This might be my bug, but it kinda looks like creating graphs with custom equality/hash semantics can result in duplicates. For instance, from the bifurcan-clj test suite:

  (testing "custom equality/hash"
    ; Very weird: I'm not sure why we get duplicate vertices here. Bug in
    ; bifurcan maybe?
    (is (= {:x #{:y "y"}
            :y #{:x "x"}}
           (-> (g/graph #(hash (name %)) (fn [a b] (= (name a) (name b))))
               (g/link :x :y)
               (g/link "y" "x")
               datafy)))))