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

This slows terminal emulation slightly.

This may be useful for users who find prediction's activity right of
the cursor distracting.

Prediction underscoring is still a little weird sometimes, it replays
a history of known/unknown changes as acks come in from the server.

Fixes #482, memory use blowup on large pastes.  mosh is still pretty slow
about copying pastes through, though.

Consolidate multiple printfs.
Break up multiline strings with string concatentation, for better
 clarity and shorter lines.
Use fputs where appropriate.

This also has the benefit of producing a single constant string with
copyright and versions in the binaries.

This feature is particularly relevant for mosh for chrome (which also
used in windows I believe).

Recent versions of tmux master gave us an 80x23 window.  tmux has been
fixed to default to 80x24, and also to allow setting window sizes in
control mode.  These flags fortunately do not conflict with older
versions tmux.  So we use them to avoid problems going forward.

This makes it easier to attach a second client to inspect a test.

On some Linux systems this is the default. On most other operating
systems accepting IPv4 connections on a IPv6 socket only happens when
explicitly requested. Even on Linux it depends on the sysctl config.

This change makes it independent from the system's defaults whether IPv4
connections will be accepted too through the same socket.

This works around Debian kfreebsd build failures.

This fixes Debian builds which only have LC_ALL=POSIX set.

This reverts commit df4dbe0d.

This fixes #881, corrupted display of man pages with tables in tmux
2.4.

tmux 2.4+ has serious bugs with combining characters.

JuiceSSH apparently has a bug where ECH for one character (ESC [ 1 X) does
not actually erase the character, in its code that receives and interprets
Mosh state updates.  This was hidden before because Mosh <= 1.2.5 never sent
this sequence, it sent ESC [ X instead as an optimization.

Do the better optimization of sending spaces for short sequences of blanks
instead.