Support backend reference counting

src/set.c

@@ -281,6 +281,9 @@ vmod_set__fini(struct vmod_re2_set **setp)
 		if (vbit_test(set->added[REGEX], i)
 		    && set->regex[i] != NULL)
 			vmod_regex__fini(&set->regex[i]);
+		if (vbit_test(set->added[BACKEND], i)
+		    && set->backend[i] != NULL)
+			VRT_Assign_Backend(&set->backend[i], NULL);
 	}
 	for (unsigned i = 0; i < NELEMS(set->added); i++)
 		vbit_destroy(set->added[i]);
@@ -340,7 +343,8 @@ vmod_set_add(VRT_CTX, struct vmod_re2_set *set, struct VARGS(set_add) *args)
 				   VRT_BACKEND_string(args->backend));
 			return;
 		}
-		set->backend[n] = args->backend;
+		set->backend[n] = NULL;
+		VRT_Assign_Backend(&set->backend[n], args->backend);
 		vbit_set(set->added[BACKEND], n);
 	}
 	if (args->valid_integer) {