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>
diff --git a/read-cache.c b/read-cache.c
index f38471c..4ac9a03 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -92,7 +92,7 @@
 
 	if (fd >= 0) {
 		unsigned char sha1[20];
-		if (!index_fd(sha1, fd, st, 0, OBJ_BLOB, ce->name, 0))
+		if (!index_fd(sha1, fd, st, OBJ_BLOB, ce->name, 0))
 			match = hashcmp(sha1, ce->sha1);
 		/* index_fd() closed the file descriptor already */
 	}
@@ -641,7 +641,7 @@
 		return 0;
 	}
 	if (!intent_only) {
-		if (index_path(ce->sha1, path, st, 1))
+		if (index_path(ce->sha1, path, st, HASH_WRITE_OBJECT))
 			return error("unable to index file %s", path);
 	} else
 		record_intent_to_add(ce);