refactor ref status logic for pushing

refactor ref status logic for pushing

Move the logic that detects up-to-date and non-fast-forward refs to a
new function in remote.[ch], set_ref_status_for_push().

Make transport_push() invoke set_ref_status_for_push() before invoking
the push_refs() implementation. (As a side-effect, the push_refs()
implementation in transport-helper.c now knows of non-fast-forward
pushes.)

Removed logic for detecting up-to-date refs from the push_refs()
implementation in transport-helper.c, as transport_push() has already
done so for it.

Make cmd_send_pack() invoke set_ref_status_for_push() before invoking
send_pack(), as transport_push() can't do it for send_pack() here.

Mark the test on the return status of non-fast-forward push to fail.
Git now exits with success, as transport.c::transport_push() does not
check for refs with status REF_STATUS_REJECT_NONFASTFORWARD nor does it
indicate rejected pushes with its return value.

Mark the test for ref status to succeed. As mentioned earlier, refs
might be marked as non-fast-forwards, triggering the push status
printing mechanism in transport.c.

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>