More tests to show key changes

Demonstrating that a new key is chosen on every close operation.

vault.c

@@ -264,6 +264,7 @@ int main(void) {
 	 */
 	struct vault_t *vault = vault_init(64, 0.1);
 	dump(vault->data, vault->data_length);
+	for (int i = 0; i < 10; i++) {
 		if (!vault_close(vault)) {
 			fprintf(stderr, "vault close failed.\n");
 			abort();
@@ -274,6 +275,7 @@ int main(void) {
 			abort();
 		}
 		dump(vault->data, vault->data_length);
+	}
 	vault_free(vault);
 	return 0;
 }