rename archival/libunarchive -> archival/libarchive; move bz/ into it

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

archival/libarchive/header_skip.c

@@ -0,0 +1,10 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+#include "libbb.h"
+#include "archive.h"
+
+void FAST_FUNC header_skip(const file_header_t *file_header UNUSED_PARAM)
+{
+}