[stm] Remove state-handling from Futures.

We make Vernacentries.interp functional wrt state, and thus remove
state-handling from `Future`. Now, a future needs a closure if it
wants to preserve state.

Consequently, `Vernacentries.interp` takes a state, and returns the
new one.

We don't explicitly thread the state in the STM yet, instead, we
recover the state that was used before and pass it explicitly to
`interp`.

I have tested the commit with the files in interactive, but we aware
that some new bugs may appear or old ones be made more apparent.
However, I am confident that this step will improve our understanding
of bugs.

In some cases, we perform a bit more summary wrapping/unwrapping. This
will go away in future commits; informal timings for a full make:

- master:
  real	2m11,027s
  user	8m30,904s
  sys	1m0,000s

- no_futures:
  real	2m8,474s
  user	8m34,380s
  sys	0m59,156s

1 files changed, 3 insertions, 1 deletions

diff --git a/plugins/ltac/tacentries.ml b/plugins/ltac/tacentries.ml
index bcd5b388a..0bf6e3d15 100644
--- a/plugins/ltac/tacentries.ml
+++ b/plugins/ltac/tacentries.ml
@@ -468,7 +468,9 @@ let register_ltac local tacl =
     let () = List.iter iter_rec recvars in
     List.map map rfun
   in
-  let defs = Future.transactify defs () in
+  (* STATE XXX: Review what is going on here. Why does this needs
+     protection? Why is not the STM level protection enough? Fishy *)
+  let defs = States.with_state_protection defs () in
   let iter (def, tac) = match def with
   | NewTac id ->
     Tacenv.register_ltac false local id tac;