tools: add shared parent path helper

Move the common parent path extraction helper into tools.c and declare it in
net.h.

Replace the local implementations in RIGHTS, NDIR and NWTESTS with
tool_parent_path(). The helper keeps the existing behavior of uppercasing the
path and preserving a trailing volume colon for parent paths such as SYS:.

No behavior change.

nwtests.c

@@ -91,29 +91,6 @@ static void tests_mask_string(uint8 mask, char *out)
   out[8] = '\0';
 }
 
-static void tests_parent_path(char *dst, char *src, int max)
-{
-  char tmp[260];
-  char *p;
-
-  tool_upcopy(tmp, src, sizeof(tmp));
-  p = strrchr(tmp, '\\');
-  if (!p) p = strrchr(tmp, ':');
-
-  if (!p) {
-    dst[0] = '\0';
-    return;
-  }
-
-  if (*p == ':') {
-    p++;
-    *p = '\0';
-  } else {
-    *p = '\0';
-  }
-
-  strmaxcpy(dst, tmp, max - 1);
-}
 
 static void tests_print_mask(char *label, int rc, uint8 mask)
 {
@@ -2575,7 +2552,7 @@ static int tests_effright(char *path)
     tests_print_eff_row("old handle path", newhandle, 0, 0, 0);
   }
 
-  tests_parent_path(usepath, path, sizeof(usepath));
+  tool_parent_path(usepath, path, sizeof(usepath));
   newhandle = alloc_temp_dir_handle(dhandle, usepath, 0, &eff_old);
   if (newhandle >= 0) {
     dealloc_dir_handle(newhandle);