dir: convert struct sha1_stat to use object_id

Convert the declaration of struct sha1_stat. Adjust all usages of this
struct and replace hash{clr,cmp,cpy} with oid{clr,cmp,cpy} wherever
possible.  Rename it to struct oid_stat.

Rename static function load_sha1_stat to load_oid_stat.

Remove macro EMPTY_BLOB_SHA1_BIN, as it's no longer used.

Signed-off-by: Patryk Obara <patryk.obara@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/dir.h b/dir.h
index 11a047b..e7bb786 100644
--- a/dir.h
+++ b/dir.h
@@ -74,9 +74,9 @@ struct exclude_list_group {
 	struct exclude_list *el;
 };
 
-struct sha1_stat {
+struct oid_stat {
 	struct stat_data stat;
-	unsigned char sha1[20];
+	struct object_id oid;
 	int valid;
 };
 
@@ -124,8 +124,8 @@ struct untracked_cache_dir {
 };
 
 struct untracked_cache {
-	struct sha1_stat ss_info_exclude;
-	struct sha1_stat ss_excludes_file;
+	struct oid_stat ss_info_exclude;
+	struct oid_stat ss_excludes_file;
 	const char *exclude_per_dir;
 	struct strbuf ident;
 	/*
@@ -195,8 +195,8 @@ struct dir_struct {
 
 	/* Enable untracked file cache if set */
 	struct untracked_cache *untracked;
-	struct sha1_stat ss_info_exclude;
-	struct sha1_stat ss_excludes_file;
+	struct oid_stat ss_info_exclude;
+	struct oid_stat ss_excludes_file;
 	unsigned unmanaged_exclude_files;
 };