Even the one lockfile object needn't be allocated each time the
function is called. Instead, define one statically-allocated
lock_file object and reuse it for every call.
Suggested-by: Jeff King <peff@peff.net> Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu> Signed-off-by: Junio C Hamano <gitster@pobox.com>