added resolver cancellation to http_connection and udp_socket. might prevent potential shutdown stalls

src/http_connection.cpp

@@ -250,6 +250,7 @@ void http_connection::close()
 {
 	error_code ec;
 	m_timer.cancel(ec);
+	m_resolver.cancel();
 	m_limiter_timer.cancel(ec);
 	m_sock.close(ec);
 	m_hostname.clear();

src/torrent.cpp

@@ -2538,6 +2538,8 @@ namespace libtorrent
 		(*m_ses.m_logger) << time_now_string() << " completed resolve proxy hostname for: " << url << "\n";
 #endif
 
+		if (m_abort) return;
+
 		if (e || host == tcp::resolver::iterator())
 		{
 			if (m_ses.m_alerts.should_post<url_seed_alert>())
@@ -2597,6 +2599,8 @@ namespace libtorrent
 		(*m_ses.m_logger) << time_now_string() << " completed resolve: " << url << "\n";
 #endif
 
+		if (m_abort) return;
+
 		std::set<std::string>::iterator i = m_resolving_web_seeds.find(url);
 		if (i != m_resolving_web_seeds.end()) m_resolving_web_seeds.erase(i);
 
@@ -2740,6 +2744,8 @@ namespace libtorrent
 		
 		m_resolving_country = false;
 
+		if (m_abort) return;
+
 		// must be ordered in increasing order
 		static const country_entry country_map[] =
 		{

src/udp_socket.cpp

@@ -251,6 +251,7 @@ void udp_socket::close()
 	m_ipv4_sock.close(ec);
 	m_ipv6_sock.close(ec);
 	m_socks5_sock.close(ec);
+	m_resolver.cancel();
 	if (m_connection_ticket >= 0)
 	{
 		m_cc.done(m_connection_ticket);