Makefile: fix dependency on wt-status.h

Noticed by Hannes, reported by Dscho.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Makefile b/Makefile
index f08d5f7..4e36487 100644
--- a/Makefile
+++ b/Makefile
@@ -375,6 +375,7 @@
 LIB_H += tree-walk.h
 LIB_H += unpack-trees.h
 LIB_H += utf8.h
+LIB_H += wt-status.h
 
 LIB_OBJS += alias.o
 LIB_OBJS += alloc.o