Add a parameter for the struct checkout variable to check_updates()
instead of using a static global variable. Passing it explicitly makes
object ownership and usage more easily apparent. And we get rid of a
static variable; those can be problematic in library-like code.
Signed-off-by: Rene Scharfe <l.s.r@web.de> Signed-off-by: Junio C Hamano <gitster@pobox.com>