The current code is very inconsistent about which signals
are caught for doing cleanup of temporary files and lock
files. Some callsites checked only SIGINT, while others
checked a variety of death-dealing signals.

This patch factors out those signals to a single function,
and then calls it everywhere. For some sites, that means
this is a simple clean up. For others, it is an improvement
in that they will now properly clean themselves up after a
larger variety of signals.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>