[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, 3 deletions

diff --git a/kernel/term_typing.ml b/kernel/term_typing.ml
index 22e109b01..f93b24b3e 100644
--- a/kernel/term_typing.ml
+++ b/kernel/term_typing.ml
@@ -266,7 +266,7 @@ let infer_declaration (type a) ~(trust : a trust) env kn (dcl : a constant_entry
       let { const_entry_body = body; const_entry_feedback = feedback_id } = c in
       let tyj = infer_type env typ in
       let proofterm =
-        Future.chain ~pure:true body (fun ((body,uctx),side_eff) ->
+        Future.chain body (fun ((body,uctx),side_eff) ->
           let j, uctx = match trust with
           | Pure ->
             let env = push_context_set uctx env in
@@ -535,7 +535,7 @@ let export_side_effects mb env ce =
       let { const_entry_body = body } = c in
       let _, eff = Future.force body in
       let ce = DefinitionEntry { c with
-        const_entry_body = Future.chain ~pure:true body
+        const_entry_body = Future.chain body
           (fun (b_ctx, _) -> b_ctx, ()) } in
       let not_exists (c,_,_,_) =
         try ignore(Environ.lookup_constant c env); false
@@ -628,7 +628,7 @@ let translate_local_def mb env id centry =
 let translate_mind env kn mie = Indtypes.check_inductive env kn mie
 
 let inline_entry_side_effects env ce = { ce with
-  const_entry_body = Future.chain ~pure:true
+  const_entry_body = Future.chain
     ce.const_entry_body (fun ((body, ctx), side_eff) ->
       let body, ctx',_ = inline_side_effects env body ctx side_eff in
       (body, ctx'), ());