[safe-string] Enable -safe-string !

We now build Coq with `-safe-string`, which enforces functional use
of the `string` datatype. Coq was pretty safe in these regard so only
a few tweaks were needed.

- coq_makefile: build plugins with -safe-string too.
- `names.ml`: we remove `String.copy` uses, as they are not needed.

1 files changed, 1 insertions, 3 deletions

diff --git a/kernel/names.ml b/kernel/names.ml
index 831b6ad46..ee8d838da 100644
--- a/kernel/names.ml
+++ b/kernel/names.ml
@@ -57,15 +57,13 @@ struct
 
   let of_string s =
     let () = check_soft s in
-    let s = String.copy s in
     String.hcons s
 
   let of_string_soft s =
     let () = check_soft ~warn:false s in
-    let s = String.copy s in
     String.hcons s
 
-  let to_string id = String.copy id
+  let to_string id = id
 
   let print id = str id