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>

commit.c

@@ -6,6 +6,7 @@
 #include "gettext.h"
 #include "hex.h"
 #include "repository.h"
+#include "object-name.h"
 #include "object-store.h"
 #include "pkt-line.h"
 #include "utf8.h"