archive: convert struct archiver_args to object_id

Change the commit_sha1 member to be called "commit_oid" and change it to
be a pointer to struct object_id.  Additionally, update some uses of
GIT_SHA1_HEXSZ and hard-coded values to use the_hash_algo instead.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/archive-zip.c b/archive-zip.c
index 155ee4a..4d66b5b 100644
--- a/archive-zip.c
+++ b/archive-zip.c
@@ -577,7 +577,7 @@ static void write_zip64_trailer(void)
 	write_or_die(1, &locator64, ZIP64_DIR_TRAILER_LOCATOR_SIZE);
 }
 
-static void write_zip_trailer(const unsigned char *sha1)
+static void write_zip_trailer(const struct object_id *oid)
 {
 	struct zip_dir_trailer trailer;
 	int clamped = 0;
@@ -590,14 +590,14 @@ static void write_zip_trailer(const unsigned char *sha1)
 	copy_le16_clamp(trailer.entries, zip_dir_entries, &clamped);
 	copy_le32(trailer.size, zip_dir.len);
 	copy_le32_clamp(trailer.offset, zip_offset, &clamped);
-	copy_le16(trailer.comment_length, sha1 ? GIT_SHA1_HEXSZ : 0);
+	copy_le16(trailer.comment_length, oid ? the_hash_algo->hexsz : 0);
 
 	write_or_die(1, zip_dir.buf, zip_dir.len);
 	if (clamped)
 		write_zip64_trailer();
 	write_or_die(1, &trailer, ZIP_DIR_TRAILER_SIZE);
-	if (sha1)
-		write_or_die(1, sha1_to_hex(sha1), GIT_SHA1_HEXSZ);
+	if (oid)
+		write_or_die(1, oid_to_hex(oid), the_hash_algo->hexsz);
 }
 
 static void dos_time(timestamp_t *timestamp, int *dos_date, int *dos_time)
@@ -635,7 +635,7 @@ static int write_zip_archive(const struct archiver *ar,
 
 	err = write_archive_entries(args, write_zip_entry);
 	if (!err)
-		write_zip_trailer(args->commit_sha1);
+		write_zip_trailer(args->commit_oid);
 
 	strbuf_release(&zip_dir);