stackoverflow on comparisons for long linked lists

[arikheinss]

== comparisons for linked lists use recursive implementation. Since julia does, as of now, not support tail call optimization, this will lead to stack overflow errors for long lists. To reproduce try this:

using DataStructures
l = nil(Float64)
n = 100_000
for i in 1:n
    l = cons(rand(), l)
end

l2 = copy(l);

# this will crash
l == l2