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

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

archival/libarchive/seek_by_read.c

@@ -0,0 +1,16 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+
+#include "libbb.h"
+#include "archive.h"
+
+/*  If we are reading through a pipe, or from stdin then we can't lseek,
+ *  we must read and discard the data to skip over it.
+ */
+void FAST_FUNC seek_by_read(int fd, off_t amount)
+{
+	if (amount)
+		bb_copyfd_exact_size(fd, -1, amount);
+}