replace-object.h: move read_replace_refs declaration from cache.h to here

Adjust several files to be more explicit about their dependency on
replace-objects to accommodate this change.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

log-tree.c

@@ -13,6 +13,7 @@
 #include "merge-ort.h"
 #include "reflog-walk.h"
 #include "refs.h"
+#include "replace-object.h"
 #include "string-list.h"
 #include "color.h"
 #include "gpg-interface.h"