4.1 Bsd terminal handler improvements

[mark at cbosgd.UUCP]

Note that TIOCDRAIN can be emulated in 4.1BSD with TIOCOUTQ,
which returns the number of characters waiting in the queue.
You loop until it goes below the level you want (waiting until
zero may result in jerky output).  A high resolution sleep,
such as nap, or select, or the fast timer driver, helps.
TIOCOUTQ does not seem to be documented in 4.1 or 4.1c.