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

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/archival/cpio.c b/archival/cpio.c
index a2d74dc..6ab2688 100644
--- a/archival/cpio.c
+++ b/archival/cpio.c
@@ -12,7 +12,7 @@
  *
  */
 #include "libbb.h"
-#include "unarchive.h"
+#include "archive.h"
 
 /* GNU cpio 2.9 --help (abridged):