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/mailmap.c b/mailmap.c
index 14f2c0f..d62d7bf 100644
--- a/mailmap.c
+++ b/mailmap.c
@@ -2,6 +2,7 @@
 #include "environment.h"
 #include "string-list.h"
 #include "mailmap.h"
+#include "object-name.h"
 #include "object-store.h"
 #include "setup.h"