[MEDIUM] use buffer->wex instead of buffer->cex for connect timeout

It's a shame not to use buffer->wex for connection timeouts since by
definition it cannot be used till the connection is not established.
Using it instead of ->cex also makes the buffer processing more
symmetric.
diff --git a/src/backend.c b/src/backend.c
index 2d5be17..f9b6dd1 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -1826,7 +1826,7 @@
 			s->be->lbprm.server_take_conn(s->srv);
 	}
 
-	s->req->cex = tick_add_ifset(now_ms, s->be->timeout.connect);
+	s->req->wex = tick_add_ifset(now_ms, s->be->timeout.connect);
 	return SN_ERR_NONE;  /* connection is OK */
 }
 
@@ -1844,7 +1844,7 @@
 
 	if (t->conn_retries < 0) {
 		/* if not retryable anymore, let's abort */
-		t->req->cex = TICK_ETERNITY;
+		t->req->wex = TICK_ETERNITY;
 		srv_close_with_err(t, conn_err, SN_FINST_C,
 				   503, error_message(t, HTTP_ERR_503));
 		if (t->srv)
@@ -1888,7 +1888,7 @@
 			return 1;
 	    
 		case SN_ERR_INTERNAL:
-			t->req->cex = TICK_ETERNITY;
+			t->req->wex = TICK_ETERNITY;
 			srv_close_with_err(t, SN_ERR_INTERNAL, SN_FINST_C,
 					   500, error_message(t, HTTP_ERR_500));
 			if (t->srv)
@@ -1959,7 +1959,7 @@
 			goto redispatch;
 		}
 
-		t->req->cex = TICK_ETERNITY;
+		t->req->wex = TICK_ETERNITY;
 		srv_close_with_err(t, SN_ERR_SRVTO, SN_FINST_Q,
 				   503, error_message(t, HTTP_ERR_503));
 
@@ -1969,7 +1969,7 @@
 
 	case SRV_STATUS_NOSRV:
 		/* note: it is guaranteed that t->srv == NULL here */
-		t->req->cex = TICK_ETERNITY;
+		t->req->wex = TICK_ETERNITY;
 		srv_close_with_err(t, SN_ERR_SRVTO, SN_FINST_C,
 				   503, error_message(t, HTTP_ERR_503));
 
@@ -1977,14 +1977,14 @@
 		return 1;
 
 	case SRV_STATUS_QUEUED:
-		t->req->cex = tick_add_ifset(now_ms, t->be->timeout.queue);
+		t->req->wex = tick_add_ifset(now_ms, t->be->timeout.queue);
 		t->srv_state = SV_STIDLE;
 		/* do nothing else and do not wake any other session up */
 		return 1;
 
 	case SRV_STATUS_INTERNAL:
 	default:
-		t->req->cex = TICK_ETERNITY;
+		t->req->wex = TICK_ETERNITY;
 		srv_close_with_err(t, SN_ERR_INTERNAL, SN_FINST_C,
 				   500, error_message(t, HTTP_ERR_500));
 		if (t->srv)