Robustify stress2 test + use tail recursive map everywhere

[domsj]

(all .ml files are as of now required to open! Prelude)

[toolslive]

I don't think we use List.fold_right or List.merge

[aantron]

Let me know if you do decide that tail-recursive Lwt_list functions (ocsigen/lwt#347) are necessary. We can quickly add them. You should be able to pin to that Lwt commit, and it will also get released in the next release. We'll probably eventually switch to tail-recursive functions no matter what, once it's time to deal with "everything" in Lwt_list, which shouldn't be too far off.

[domsj]

We have included our own version of the Lwt_list functions ... see https://github.com/openvstorage/alba/blob/1.3.15/ocaml/src/tools/prelude.ml#L856, so no rush for a new release from our end.
As an fyi: the stress2 suite still periodically segfaults on my machine. But as it's only on my machine I'm starting to think it's a hardware problem.