#6 TTY subsystem needs work

[Christopher Williams]

The tty subsystem is incomplete. It's missing ioctl support, and its behavior is not 100% correct, particularly with handling control characters on input and output. Raw and non-canonical modes are untested and probably don't work at all. There is also duplicated code in dev_vt.c which belongs in tty.c. dev_link.c should also act as a tty device.