cp: implement -T

cp: implement -T

Implement "cp -T". Some Linux kernel Makefiles started using this recently,
so allow also building on systems using busybox cp.

function                                             old     new   delta
cp_main                                              360     428     +68
copy_file                                           1678    1676      -2
packed_usage                                       32290   32259     -31
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/2 up/down: 76/-39)             Total: 35 bytes

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>