tty patch: centralization of DTRWAIT

[Poul-Henning Kamp]

http://phk.freebsd.dk/patch/tty.patch

This patch centralizes the DTRWAIT functionality and adds a ttygone()
function which signals hardware detachment to the central tty code.

Please test & review.

Affected files:
	Index: dev/cx/if_cx.c
	Index: dev/cy/cy.c
	Index: dev/digi/digi.c
	Index: dev/digi/digi.h
	Index: dev/rc/rc.c
	Index: dev/rp/rp.c
	Index: dev/rp/rpvar.h
	Index: dev/si/si.c
	Index: dev/si/si.h
	Index: dev/sio/sio.c
	Index: dev/sx/sx.c
	Index: dev/sx/sx.h
	Index: kern/tty.c
	Index: pc98/pc98/sio.c
	Index: sys/tty.h


-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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