MINOR: server: add a list of already used idle connections

There's a difference with the other idle conns in that these new
ones have already been used and may be reused by other streams.
diff --git a/src/hlua.c b/src/hlua.c
index 08831ab..df3904f 100644
--- a/src/hlua.c
+++ b/src/hlua.c
@@ -5061,6 +5061,7 @@
 	LIST_INIT(&socket_tcp.actconns);
 	LIST_INIT(&socket_tcp.pendconns);
 	LIST_INIT(&socket_tcp.priv_conns);
+	LIST_INIT(&socket_tcp.idle_conns);
 	socket_tcp.state = SRV_ST_RUNNING; /* early server setup */
 	socket_tcp.last_change = 0;
 	socket_tcp.id = "LUA-TCP-CONN";
@@ -5105,6 +5106,7 @@
 	LIST_INIT(&socket_ssl.actconns);
 	LIST_INIT(&socket_ssl.pendconns);
 	LIST_INIT(&socket_ssl.priv_conns);
+	LIST_INIT(&socket_ssl.idle_conns);
 	socket_ssl.state = SRV_ST_RUNNING; /* early server setup */
 	socket_ssl.last_change = 0;
 	socket_ssl.id = "LUA-SSL-CONN";