ocaml-batteries-team/batteries-included — pull request #426 by zakki (2013-08-04 07:54:09+00:00)
Title: Fix BatMutex.DebugMutex.id is always 0.

Perhaps DebugMutex.unique intends to be closure, but it is constant now.
```ocaml
open Batteries
module Mutex = BatMutex.DebugMutex

let _ =
let m = Mutex.create () in
let m2 = Mutex.create () in
Mutex.lock m;
Mutex.lock m2;
Mutex.unlock m2;
Mutex.unlock m;
()
```