Use ISIG flag for our stty call from jline, in order to translate INT to ^C.
ISIG was added in "Add interrupt and quit keys" (d7292625).

This is related to issue #53.

Reviewed-by: Tomasz Grabiec <tgrabiec@gmail.com>
Signed-off-by: Or Cohen <orc@fewbytes.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>