tree_poproot
while ((tree_poproot(&relay->connectors, NULL, (void**)&c)))
while (tree_poproot(&hs->deferred, &evpid, NULL)) {
while (tree_poproot(&hs->deferred, NULL, NULL))
if (tree_poproot(&flush_evp, NULL, (void**)(&e))) {
while (tree_poproot(&messages, &evpid, (void**)&evp)) {
while (tree_poproot(&update->messages, &id, (void*)&message)) {
int tree_poproot(struct tree *, uint64_t *, void **);