send-pack: do not give up when remote has insanely large number of refs.

send-pack: do not give up when remote has insanely large number of refs.

Stephen C. Tweedie noticed that we give up running rev-list when
we see too many refs on the remote side.  Limit the number of
negative references we give to rev-list and continue.

Not sending any negative references to rev-list is very bad --
we may be pushing a ref that is new to the other end.

Signed-off-by: Junio C Hamano <junkio@cox.net>