string constants

<Someone> wrote:
> Linux, Redhat 7.1 nethack 3.4.0
>
>Please see attached patch file.
>
>I'm attempting to move more stuff into the "read-only" area, in
>preparation for a port to another OS.

src/detect.c

@@ -753,7 +753,7 @@ d_level *where;
 	    else	return "near you";
 }
 
-static struct {
+static const struct {
     const char *what;
     d_level *where;
 } level_detects[] = {