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>

builtin-commit.c

@@ -320,7 +320,8 @@ static char *prepare_index(int argc, const char **argv, const char *prefix)
 		die("unable to write new_index file");
 
 	fd = hold_lock_file_for_update(&false_lock,
-				       git_path("next-index-%d", getpid()), 1);
+				       git_path("next-index-%d", getpid()),
+				       LOCK_DIE_ON_ERROR);
 
 	create_base_index();
 	add_remove_files(&partial);