Remove trailing underscore from fhandler_base and friends, throughout.

Remove trailing underscore from fhandler_base and friends, throughout.
* fhandler.h (fhandler_base::set_open_status): New method.  Stores original
open status.
(fhandler_base::get_open_status): New method.  Retrieves original open status.
(fhandler_base::reset_to_open_binmode): New method.
* fhandler.cc (fhandler_base::open): Save open status.
(fhandler_base::init): Ditto.
* fhandler_clipboard.cc (fhandler_clipboard::open): Ditto.
* fhandler_console.cc (fhandler_console::open): Ditto.
* fhandler_dsp.cc (fhandler_dsp::open): Ditto.
* fhandler_dev_mem.cc (fhandler_dev_mem::open): Ditto.
* fhandler_dev_random.cc (fhandler_dev_random::open): Ditto.
* fhandler_serial.cc (fhandler_serial::open): Ditto.
* fhandler_tty_slave.cc (fhandler_tty_slave::open): Ditto.
* fhandler_tty_master.cc (fhandler_tty_master::open): Ditto.
* fhandler_dev_zero.cc (fhandler_dev_zero::open): Ditto.
* syscalls.cc (setmode): Rework so that 0 mode value causes reversion to open
state.
* fhandler_tty_slave.cc (fhandler_tty_slave::read): Use correct multiplier when
converting from deciseconds to milliseconds.