Instead of dying of a segmentation fault if getcwd() returns NULL, use
xgetcwd() to make sure to write a useful error message and then exit
in an orderly fashion.
Suggested-by: Jeff King <peff@peff.net> Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>