* dcrt0.cc (dll_crt0_0): Call tty_list::init_session here.

* dcrt0.cc (dll_crt0_0): Call tty_list::init_session here.
(dll_crt0_1): Reflect renaming from tty_init to tty::init_session.
(do_exit): Reflect moving of tty_terminate into tty_list.
* exceptions.cc (events_init): Move tty_mutex stuff elsewhere.
* fhandler_console.cc (set_console_title): Use lock_ttys class.
* fhandler_termios.cc (fhandler_termios::bg_check): Make debug output more
accurate.
* fhandler_tty.cc (fhandler_tty_slave::open): Reflect move of attach_tty into
tty_list class.  Don't attempt to grab master end of pty if master doesn't
exist.
(fhandler_pty_master::open): Reflect move of allocate_tty into tty_list class.
Use lock_ttys::release to release mutex.  Improve debugging output.
(fhandler_pty_master::setup): Remove if 0'ed block.  Fix argument to
SetNamedPipeHandleState.
* pinfo.cc (_pinfo::set_ctty): Lock ttys before setting sid/pgid.  Improve
debugging.  Add temporary debugging.
* tty.cc (tty_list::init_session): New function.
(tty::init_session): Rename from tty_init.  Reflect move of attach_tty to
tty_list class.
(tty::create_master): Rename from create_tty_master.
(tty_list::attach): Rename from attach_tty.  Reflect renaming of connect_tty to
connect.  Ditto for allocate_tty.
(tty_terminate): Delete.
(tty_list::terminate): Subsume tty_terminate.  Use lock_ttys rather than
manipulating mutex directly.
(tty_list::allocate): Rename from allocate_tty.  Use lock_ttys rather than
manipulating mutex directly.  Don't set sid here since linux apparently doesn't
do this.  Reflect move of create_tty_master into tty.
(lock_ttys::lock_ttys): Define new constructor.
(lock_ttys::release): New function.
* tty.h (tty::exists): Return false immediately if !master_pid.
(tty::set_master_closed): Define new function.
(tty::create_master): Ditto.
(tty::init_session): Ditto.
(tty_list::mutex): New field.
(tty_list::allocate): Define new function.
(tty_list::connect): Ditto.
(tty_list::attach): Ditto.
(tty_list::init_session): Ditto.
(lock_ttys): New class.
(tty_init): Delete declaration.
(tty_terminate): Ditto.
(attach_tty): Ditto.
(create_tty_master): Ditto.