Fix Data.List.Lazy iterate

[ibara1454]

A solution of #140

Here's the result of the modification of iterate.
All the values are evaluated exactly once.

It still has a bug. Because the result of take 3 lazyl should be

> take 3 lazyl
1
2
fromStrict ((Cons 0 (Cons 1 (Cons 2 Nil))))

Not

> take 3 lazyl
1
2
3
fromStrict ((Cons 0 (Cons 1 (Cons 2 Nil))))

But the bug is made by take (as #138), not iterate. So we have nothing to do with this.

Just to be sure, I made a performance comparison between the before and after of iterate.
It is made by compiling the purescript code into javascript, and then run the benchmark by Benchmark.js.

Each value in this benchmark is the time of the calculation sum $ take n $ iterate (_ + 1) 1, where n is the length of list in the benchmark.

The old iterate has no value after length > 5000, because it throws exceptions by maximum call stack size exceeded. Yes, it is not stack-safe.

The old iterate run extremely slow in PSCi (time complexity is not linear), but (I don't know why) it is not bad (except the stack overflow) in this benchmark.

[ibara1454]

The bug is based on fix.