extend_file need continue when the file exists

Jens,

If some testing files exist and some others don't exist, fio will
report failure on the no-exist file. Here is a patch to fix it.

-yanmin

---
diff -Nraup fio/filesetup.c fio_work/filesetup.c
--- fio/filesetup.c	2008-02-25 14:25:10.000000000 +0800
+++ fio_work/filesetup.c	2008-02-26 10:11:15.000000000 +0800
@@ -34,7 +34,7 @@ static int extend_file(struct thread_dat
 		unlink_file = 1;
 
 	if (unlink_file || new_layout) {
-		if (unlink(f->file_name) < 0) {
+		if ((unlink(f->file_name) < 0) && (errno != ENOENT)) {
 			td_verror(td, errno, "unlink");
 			return 1;
 		}