daemon: Send TTYs directly when SUPERUSER_SEND_TTY is set.

Enables reuse of the existing terminal instead of creating a proxy PTY.

Warning: Reuse of existing terminal breaks job control in the caller shell,
thus SUPERUSER_SEND_TTY should not be enabled by default unless the caller
shell is patched to reclaim the controlling terminal.
Merge pull request #222 from mkasick/master

daemon: Send TTYs directly when SUPERUSER_SEND_TTY is set.