object-name.h: move declarations for object-name.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/checkout.c b/checkout.c
index 1247b88..9235073 100644
--- a/checkout.c
+++ b/checkout.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "object-name.h"
 #include "remote.h"
 #include "refspec.h"
 #include "checkout.h"