* Carrier detect (TS_CARR_ON) is based on the actual DCD bit, even if it's
being ignored.
* Set TS_WOPEN early on in zsopen().
* Don't disable interrupts on the console during close if we have DDB.
Inert changes:
* Don't handle ZS_HWFLAG_NO_DCD here; the frontend does it.
* Deprecate `register'.
* Use SET(), CLR(), and ISSET().
More performance changes:
* Rototill receive handling; use a backpressure mechanism to prevent livelock.
* Output silo/ibuf overflow warnings at most once per minute, from a callout.
* When we exhaust the current transmit run, turn off transmit interrupts in
zstty_txint(), so we're fairly sure we don't get another one.
7d7ecb9200