test-terminal: set output terminals to raw mode

test-terminal: set output terminals to raw mode

Not setting them to raw mode causes funny things to happen, such as
\n -> \r\n translation:

  ./test-terminal.perl echo foo | xxd
  0000000: 666f 6f0d 0a                             foo..

(Notice the added 0d.)

To avoid this, set the (pseudo)terminal to raw mode.  Note that the
IO::Pty docs recommend doing it on both master and slave.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Acked-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>