* ports.c, ports.h (scm_make_port_type): New interface for

* ports.c, ports.h (scm_make_port_type): New interface for
creation of port types (replaces scm_newptob).  Just as for the
smobs, we need to separate the internal representation of smob
types from the interface, so that we easily can add new fields and
rearrange things without caring about backward compatibility.
This change was forced by the need in GOOPS to create classes
representing port types.
(scm_set_ptob_mark, scm_set_ptob_free, scm_set_ptob_print,
scm_set_ptob_equalp, scm_set_ptob_flush_input, scm_set_ptob_close,
scm_set_ptob_seek, scm_set_ptob_truncate,
scm_set_ptob_input_waiting_p): New setters.
(scm_newptob): Rewritten to use scm_make_port_type.  For backward
compatibility.
(scm_ptobs): Changed type scm_ptobfuns --> scm_ptob_descriptor.
(scm_prinport): Removed.
(scm_port_print): Added.
(scm_print_port_mode): Added.
(void_port_ptob, print_void_port, close_void_port, noop0):
Removed.  Removed #include "genio.h" Added #include "objects.h",
#include "smobs.h"