Add cmdline_api_version to --config output

This gives to reverse-dependencies the ability to auto-detect which
command-line syntax to use.

src/params.ml

@@ -477,6 +477,7 @@ let configuration toolbox force =
   in
   let lines =
     [ "version == \"" ^ rawversion () ^ "\""
+    ; "cmdline_api_version == 2"
     ; "built_with == \"OCaml " ^ Sys.ocaml_version ^ "\""
     ; "tlapm_executable == \"" ^ Sys.executable_name ^ "\""
     ; "max_threads == " ^ string_of_int !max_threads