syncronize input on master tty with slave tty.
* fhandler_tty.cc (fhandler_pty_master::accept_input): Use them to
syncronize with slave.
* fhandler_tty.cc (fhandler_tty_slave::read): Use input mutex and
event to syncronize with master. Do not limit amount of data read
from master to vmin value. Interrupt on signal and return already
read data, if any.
* fhandler_tty.cc (fhandler_tty_slave::open): Handle input mutex and
event.
* fhandler_tty.cc (fhandler_tty_common::close): Ditto.
* fhandler_tty.cc (fhandler_tty_common::set_close_on_exec): Ditto.
* fhandler_tty.cc (fhandler_tty_common::fixup_after_fork): Ditto.
* fhandler_tty.cc (fhandler_tty_common::dup): Ditto.
* tty.h (tty::open_input_mutex): New function.
* tty.cc (tty::common_init): Create input mutex and event.
Include sys/termios.h for files which need it.
* tty.h: New file.
* shared_info.h: New file.
* fhandler.h: Move inline methods that rely on tty stuff to
fhandler_console.cc.
* fhandler_tty.cc (fhandler_pty_master::process_slave_output): Set
output_done_event immediately after reading data to speed up tty output
processing.
(process_output): Set write_error to errno or zero.
(fhandler_tty_slave::write): Check previous write error prior to writing to
slave end of pipe. This allows tty output to be slightly less synchronous.
* fhandler_console.cc (fhandler_console::tcsetpgrp): Moved here from
fhandler.h.
(fhandler_console::set_input_state): Ditto.