object-file.h: move declarations for object-file.c functions from cache.h

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/cache-tree.c b/cache-tree.c
index 39f0c74..ebfe649 100644
--- a/cache-tree.c
+++ b/cache-tree.c
@@ -7,6 +7,7 @@
 #include "tree-walk.h"
 #include "cache-tree.h"
 #include "bulk-checkin.h"
+#include "object-file.h"
 #include "object-store.h"
 #include "replace-object.h"
 #include "promisor-remote.h"