Fix of failure in_of_string on Windows.

The file of the form "file:line:col1:col2" was created, than split on ":"
and and int_of_string was used to get line number and colon numbers. This
failed on windows because the file name contained ':', i.e.,
"C:\...\gnatprove\p\..\p.mlw:2254:55:150".

src/transform/intro_vc_vars_counterexmp.ml

@@ -194,16 +194,27 @@ let () = Trans.register_transform "intro_vc_vars_counterexmp"
   intro_vc_vars_counterexmp
   ~desc:"Introduce."
 
+let rec string_join sep l =
+  match l with
+  | [] -> ""
+  | [x] -> x
+  | x :: rest -> x ^ sep ^ string_join sep rest
+
 let get_location_of_vc task =
   let meta_args = Task.on_meta_excl meta_vc_location task in
   match meta_args with
   | Some [Theory.MAstr loc_str] ->
-    let splitted = Strings.bounded_split ':' loc_str 4 in
-    let loc =  match splitted with
-      | [filename; line; col1; col2] ->
+    (* There may be colons in the file name. We still split on the colon, look at
+       the last three elements, and put the remaining ones back together to form the
+       file name. We may lose colons at the beginning or end of the filename, but
+       even on windows that's not allowed. *)
+    let split = Strings.rev_split ':' loc_str in
+    let loc =  match split with
+      | col2 :: col1 :: line :: (_ :: _) as rest ->
 	let line = int_of_string line in
 	let col1 = int_of_string col1 in
 	let col2 = int_of_string col2 in
+	let filename = string_join ":" (List.rev rest) in
         Some (Loc.user_position filename line col1 col2)
       | _ -> None in
     loc