use xopen() to handle fatal open(2) failures

Add and apply a semantic patch for using xopen() instead of calling
open(2) and die() or die_errno() explicitly.  This makes the error
messages more consistent and shortens the code.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/update-index.c

@@ -95,9 +95,7 @@ static int create_file(const char *path)
 {
 	int fd;
 	path = get_mtime_path(path);
-	fd = open(path, O_CREAT | O_RDWR, 0644);
-	if (fd < 0)
-		die_errno(_("failed to create file %s"), path);
+	fd = xopen(path, O_CREAT | O_RDWR, 0644);
 	return fd;
 }