index_fd(): turn write_object and format_check arguments into one flag

The "format_check" parameter tucked after the existing parameters is too
ugly an afterthought to live in any reasonable API.

Combine it with the other boolean parameter "write_object" into a single
"flags" parameter.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/hash-object.c

@@ -14,8 +14,11 @@ static void hash_fd(int fd, const char *type, int write_object, const char *path
 {
 	struct stat st;
 	unsigned char sha1[20];
+	unsigned flags = (HASH_FORMAT_CHECK |
+			  (write_object ? HASH_WRITE_OBJECT : 0));
+
 	if (fstat(fd, &st) < 0 ||
-	    index_fd(sha1, fd, &st, write_object, type_from_string(type), path, 1))
+	    index_fd(sha1, fd, &st, type_from_string(type), path, flags))
 		die(write_object
 		    ? "Unable to add %s to database"
 		    : "Unable to hash %s", path);