Change time limit computation.

For a measured time of 0.49 second, a prover would only get 1 second to
replay the proof, i.e., half of the expected 1.98 seconds. The time limit
is now rounded to nearest to prevent this underestimation on fast proofs.

src/session/controller_itp.ml

@@ -332,7 +332,7 @@ let adapt_limits ~interactive ~use_steps limits a =
        (* increased time limit is 1 + twice the previous running time,
        but enforced to remain inside the interval [l,2l] where l is
        the previous time limit *)
-       let t = truncate (1.0 +. 2.0 *. t) in
+       let t = truncate (1.5 +. 2.0 *. t) in
        let increased_time = if interactive then 0
                             else max timelimit (min t (2 * timelimit)) in
        (* increased mem limit is just 1.5 times the previous mem limit *)