* dtable.cc (dtable::build_fhandler): Issue internal error on unknown device.

* dtable.cc (dtable::build_fhandler): Issue internal error on unknown device.
* fhandler.cc (fhandler_base::close): Show both name and handle in debugging
output.
* fhandler.h (fhandler_base::get_guard): New virtual method.
(fhandler_pipe::get_guard): New method.
(fhandler_socket::ready_for_read): Delete declaration.
(fhandler_pipe::ready_for_read): Ditto.
(fhandler_serial::ready_for_read): Ditto.
(fhandler_console::ready_for_read): Ditto.
(fhandler_tty_common::ready_for_read): Ditto.
(fhandler_windows::ready_for_read): Ditto.
(struct select_record::peek): Declare new method.
* select.cc (MAKEready): Delete.
(peek_pipe): Use get_guard method to retrieve potential guard mutex handle.
(fhandler_base::ready_for_read): Rewrite as generic ready-for-read handler.
Should only be called for "slow" devices.
(fhandler_socket::ready_for_read): Delete definition.
(fhandler_pipe::ready_for_read): Ditto.
(fhandler_serial::ready_for_read): Ditto.
(fhandler_console::ready_for_read): Ditto.
(fhandler_tty_common::ready_for_read): Ditto.
(fhandler_windows::ready_for_read): Ditto.
(fhandler_pipe::select_read): Fill in new peek record in select_record
structure.
(fhandler_console::select_read): Ditto.
(fhandler_tty_common::select_read): Ditto.
(fhandler_serial::select_read): Ditto.
(fhandler_socket::select_read): Ditto.
(fhandler_socket::select_read): Ditto.
(fhandler_tty_slave::ready_for_read): Check for tty not open.  Set errnos
appropriately.
* syscalls.cc (_read): Allow ready_for_read to set errno.
* pinfo.cc (pinfo::init): Return spawn/NO_WAIT process as valid if it is
initializing.
* sigproc.cc (getsem): Adjust wait for process to initialize downward to avoid
huge waits.