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/builtin/merge-recursive.c b/builtin/merge-recursive.c
index 25f42f2..fa10354 100644
--- a/builtin/merge-recursive.c
+++ b/builtin/merge-recursive.c
@@ -5,6 +5,7 @@
 #include "gettext.h"
 #include "tag.h"
 #include "merge-recursive.h"
+#include "object-name.h"
 #include "xdiff-interface.h"
 
 static const char builtin_merge_recursive_usage[] =