Merge of r4654, r4672, r4684, r4685, r4692: resolver changes. *) Resolver: fixed format specification. Patch by Yichun Zhang (agentzh). *) Support for IPv6 literals and an optional port in resolver. *) Fixed crash in ngx_resolver_cleanup_tree(). If sending a DNS request fails with an error (e.g., when mistakenly trying to send it to a local IP broadcast), such a request is not deleted if there are clients waiting on it. However, it was still erroneously removed from the queue. Later ngx_resolver_cleanup_tree() attempted to remove it from the queue again that resulted in a NULL pointer dereference. *) When "resolver" is configured with a domain name, only the first resolved address was used. Now all addresses will be used. *) Fixed segfault with poll and resolver used. Poll event method needs ngx_cycle->files to work, and use of ngx_exit_cycle without files set caused null pointer dereference in resolver's cleanup on udp socket close.