Replace x86-64 paccept with accept4

This patch changes the paccept syscall to accept4 for x86-64, since
the former was dropped in Linux kernel commit v2.6.27-rc7-14-g2d4c826.
At the same time, it adds support for pretty printing its arguments.

* linux/x86_64/syscallent.h: Replace paccept with accept4,
hook in sys_accept4.
* net.c (sys_accept): Leave a small stub calling the new...
(do_accept): ... function, which also adds a flags_arg argument.
(sys_accept4): New.
diff --git a/net.c b/net.c
index 9759268..9d2b9f9 100644
--- a/net.c
+++ b/net.c
@@ -1303,13 +1303,14 @@
 	return 0;
 }
 
-int
-sys_accept(tcp)
-struct tcb *tcp;
+static int
+do_accept(struct tcb *tcp, int flags_arg)
 {
 	if (entering(tcp)) {
 		tprintf("%ld, ", tcp->u_arg[0]);
-	} else if (!tcp->u_arg[2])
+		return 0;
+	}
+	if (!tcp->u_arg[2])
 		tprintf("%#lx, NULL", tcp->u_arg[1]);
 	else {
 		int len;
@@ -1322,10 +1323,29 @@
 		tprintf(", ");
 		printnum_int(tcp, tcp->u_arg[2], "%u");
 	}
+	if (flags_arg >= 0) {
+		tprintf(", ");
+		printflags(sock_type_flags, tcp->u_arg[flags_arg],
+			   "SOCK_???");
+	}
 	return 0;
 }
 
 int
+sys_accept(struct tcb *tcp)
+{
+	return do_accept(tcp, -1);
+}
+
+#ifdef LINUX
+int
+sys_accept4(struct tcb *tcp)
+{
+	return do_accept(tcp, 3);
+}
+#endif
+
+int
 sys_send(tcp)
 struct tcb *tcp;
 {