message: Fix irmin checkout & commit times
diff: @@ -439,7 +439,7 @@ impl Timing {
  }
  self.tezedge_checkout_stats.add_time(tezedge_time);
  - self.irmin_checkout_stats.add_time(tezedge_time);
  + self.irmin_checkout_stats.add_time(irmin_time);
  self.set_current_context(context_hash)?;
  self.checkout_time = Some((irmin_time, tezedge_time));
  @@ -452,7 +452,7 @@ impl Timing {
  }
  self.tezedge_commit_stats.add_time(tezedge_time);
  - self.irmin_commit_stats.add_time(tezedge_time);
  + self.irmin_commit_stats.add_time(irmin_time);
  self.sync_global_stats(irmin_time, tezedge_time)?;
  self.sync_block_stats()?;
  