refs/ref-cache.h: add missing declarations (hdr-check)

Signed-off-by: Ramsay Jones <ramsay@ramsayjones.plus.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/ref-cache.h

@@ -1,7 +1,10 @@
 #ifndef REFS_REF_CACHE_H
 #define REFS_REF_CACHE_H
 
+#include "cache.h"
+
 struct ref_dir;
+struct ref_store;
 
 /*
  * If this ref_cache is filled lazily, this function is used to load