prefer xwrite instead of write

prefer xwrite instead of write

Our xwrite wrapper already deals with a few potential hazards, and
are as such more robust. Prefer it instead of write to get the
robustness benefits everywhere.

Signed-off-by: Erik Faye-Lund <redacted>
Reviewed-and-improved-by: Jonathan Nieder <redacted>
Signed-off-by: Junio C Hamano <redacted>