This reverts commit 45c521d6.

The root problem here is that writes to the frame buffer may alter it,
but leave it with the same contents as before, and the diff between
the two states is the empty string.  With the dirty-rows,
smart-pointer changes to Framebuffer, it is easy to run into this
situation.  This got Network::TransportSender confused about timeouts,
and mosh-server would spin.

The theoretically correct fix would be to have operator==() exactly
correspond to diff(otherstate).empty().  I have partly implemented
this (and may yet finish) but it's not trivial to get right.

This is a much simpler fix that simply attempts to correctly update
timers when two framebuffers are different and an empty diff is
generated.

This is not a fix for bad timeouts, but rather a band-aid
to keep Mosh from consuming large amounts of CPU time.

This helps with #819.

Fixes #821, OS X abnormal exit on client input at mosh-server
shutdown.  On OpenIndiana, TIOCG[GS]WINSZ also fail in this situation.

Some systems do not deliver SIGPIPE to shell pipeline writers when the
downstream reader has exited.  So, also check for errors from
/bin/printf.  I fixed this for OpenBSD 6.0 but I think it will also
fix posh on Linux.

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

Resolves #786.

Replace some blind timeouts with actual synchronization.
Improve performance on some slow tests.
Tweak some of the remaining timeouts.

This still isn't good enough to get 'make -j9 check'
working reliably on Cygwin for me; I think some Cygwin/
Windows scheduling issues remain.

See https://github.com/tmux/tmux/issues/539

This also serves nicely as documentation of the Cygwin build
requirements.

Discovered with OpenBSD 6.0 /bin/sh

Fixes #788.

This also works around issues with remote pty typeahead echo corrupting output
from mosh-server.

This eliminates issues with typeahead being echoed by the remote pty
and corrupting remote output from mosh-server to the mosh script, but
cannot be made default because older mosh-servers require a pty.

It looks like Mosh used to be able to do this but the capability was
lost when port ranges were added in 141ec239.

Also cleans up other setsockopt() calls, and buffer sizing/handling
for recvmsg().

These are minor errors and no actual misbehavior was observed.
Discovered while working Windows Subsystem for Linux compatibility
issues.

This moves all routine stdout/stderr output into the parent
server, and adds tcdrain(), even though this may be a
FreeBSD pty bug.

This is an old, old bug.

If #mosh ever sets the +n channel mode, we'll need to remove the
`skip_join: true` part