strace in ocamltest: take reviewer comments into account

ocamltest/actions_helpers.ml

@@ -115,7 +115,7 @@ let run_cmd
       in
       let strace_flags = Environments.safe_lookup Strace.strace_flags env in
       let strace_cmd =
-        ["strace -f -o"; strace_logfile; strace_flags]
+        ["strace"; "-f"; "-o"; strace_logfile; strace_flags]
       in
       strace_cmd @ original_cmd
     end else original_cmd

ocamltest/strace.ml

@@ -24,7 +24,7 @@ let (counters : (string, int) Hashtbl.t) = Hashtbl.create 10
 let get_logfile_name base =
   let n = try Hashtbl.find counters base with Not_found -> 1 in
   let filename = Printf.sprintf "strace-%s_%d.log" base n in
-  Hashtbl.add counters base (n+1);
+  Hashtbl.replace counters base (n+1);
   filename
 
 let _ =