Merged changes from 2.0 version (revisions 1.46-1.50) by hand.
Finished conversion to clists: removed flush of tty output buffer
in comflush() (most writes were truncated to 256 bytes) and restored
bypass of ttyinput() in siopoll().
Finished conversion to 2.0 types - more void *'s, less caddr_t's,
less casts, no Dev_t's.
Only these things are seriously broken now compared with 1.1.5:
waiting for output complete is impossible so ttywait() can deadlock;
sioclose() isn't called enough so sioopen() sometimes returns EBUSY
unnecessarily; input flow control is not implemented.
3e0a35fee4