t: rename t2014-switch.sh to t2014-checkout-switch.sh

The old name does not really say that this is about 'checkout -b'. See 49d833dc07 (Revert "checkout branch: prime cache-tree fully" - 2009-05-12) for more information Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>