use mrb_intern_str instead of mrb_intern if possible

src/class.c

@@ -1226,7 +1226,7 @@ static mrb_sym
 mrb_sym_value(mrb_state *mrb, mrb_value val)
 {
   if(val.tt == MRB_TT_STRING) {
-    return mrb_intern(mrb, RSTRING_PTR(val));
+    return mrb_intern_str(mrb, val);
   }
   else if(val.tt != MRB_TT_SYMBOL) {
     mrb_value obj = mrb_funcall(mrb, val, "inspect", 0);

src/sprintf.c

@@ -613,7 +613,7 @@ retry:
                (int)(p - start + 1), start, mrb_sym2name(mrb, id));
         }
         symname = mrb_str_new(mrb, start + 1, p - start - 1);
-        id = mrb_intern(mrb, RSTRING_PTR(symname));
+        id = mrb_intern_str(mrb, symname);
         nextvalue = GETNAMEARG(mrb_symbol_value(id), start, (int)(p - start + 1));
         if (UNDEF_P(nextvalue)) {
           mrb_raise(mrb, E_KEY_ERROR, "key%.*s not found", (int)(p - start + 1), start);