Enhance hold_lock_file_for_{update,append}() API

This changes the "die_on_error" boolean parameter to a mere "flags", and
changes the existing callers of hold_lock_file_for_update/append()
functions to pass LOCK_DIE_ON_ERROR.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/pack-refs.c b/pack-refs.c
index 848d311..2c76fb1 100644
--- a/pack-refs.c
+++ b/pack-refs.c
@@ -89,7 +89,8 @@
 	memset(&cbdata, 0, sizeof(cbdata));
 	cbdata.flags = flags;
 
-	fd = hold_lock_file_for_update(&packed, git_path("packed-refs"), 1);
+	fd = hold_lock_file_for_update(&packed, git_path("packed-refs"),
+				       LOCK_DIE_ON_ERROR);
 	cbdata.refs_file = fdopen(fd, "w");
 	if (!cbdata.refs_file)
 		die("unable to create ref-pack file structure (%s)",