unpack-trees: pass checkout state explicitly to check_updates()

Add a parameter for the struct checkout variable to check_updates()
instead of using a static global variable.  Passing it explicitly makes
object ownership and usage more easily apparent.  And we get rid of a
static variable; those can be problematic in library-like code.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

unpack-trees.c

@@ -218,8 +218,8 @@ static void unlink_entry(const struct cache_entry *ce)
 	schedule_dir_for_removal(ce->name, ce_namelen(ce));
 }
 
-static struct checkout state;
+static int check_updates(struct unpack_trees_options *o,
-static int check_updates(struct unpack_trees_options *o)
+			 const struct checkout *state)
 {
 	unsigned cnt = 0, total = 0;
 	struct progress *progress = NULL;
@@ -264,7 +264,7 @@ static int check_updates(struct unpack_trees_options *o)
 			display_progress(progress, ++cnt);
 			ce->ce_flags &= ~CE_UPDATE;
 			if (o->update && !o->dry_run) {
-				errs |= checkout_entry(ce, &state, NULL);
+				errs |= checkout_entry(ce, state, NULL);
 			}
 		}
 	}
@@ -1094,6 +1094,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	int i, ret;
 	static struct cache_entry *dfc;
 	struct exclude_list el;
+	struct checkout state;
 
 	if (len > MAX_UNPACK_TREES)
 		die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
@@ -1239,7 +1240,7 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
 	}
 
 	o->src_index = NULL;
-	ret = check_updates(o) ? (-2) : 0;
+	ret = check_updates(o, &state) ? (-2) : 0;
 	if (o->dst_index) {
 		if (!ret) {
 			if (!o->result.cache_tree)