Enable wt-status to run against non-standard index file.

We still default to get_index_file(), but this can be overridden
by setting wt_status.index_file after calling wt_status_prepare().

Signed-off-by: Kristian Høgsberg <krh@redhat.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

wt-status.c

@@ -53,6 +53,7 @@ void wt_status_prepare(struct wt_status *s)
 	s->branch = head ? xstrdup(head) : NULL;
 	s->reference = "HEAD";
 	s->fp = stdout;
+	s->index_file = get_index_file();
 }
 
 static void wt_status_print_cached_header(struct wt_status *s)
@@ -198,7 +199,7 @@ static void wt_status_print_changed_cb(struct diff_queue_struct *q,
 static void wt_read_cache(struct wt_status *s)
 {
 	discard_cache();
-	read_cache();
+	read_cache_from(s->index_file);
 }
 
 static void wt_status_print_initial(struct wt_status *s)

wt-status.h

@@ -21,6 +21,7 @@ struct wt_status {
 	int commitable;
 	int workdir_dirty;
 	int workdir_untracked;
+	const char *index_file;
 	FILE *fp;
 };