(io_select, io_init, io_open, io_close, io_output, io_flush, io_write,

(io_select, io_init, io_open, io_close, io_output, io_flush, io_write,
io_puts, iom_create, iom_getmask, iom_set, iom_clear, iom_zero):
Portability bug: io_select() passed bit_fdmask to select().  This
breaks the fd_set abstraction, and works only with the traditional
Unix implementation of fd_set.  Use fd_set and its operations instead.
Remove unused source files.  Note: the offending code is currently
unsued.  But it's a time bomb, and fixing it also replaces a bunch of
code by standard library services.