Load port bindings in separate (ice-9 ports) module

* module/ice-9/ports.scm: New file.
* am/bootstrap.am (SOURCES): Add ice-9/ports.scm.
* libguile/fports.c (scm_init_ice_9_fports): New function.
  (scm_init_fports): Arrange for scm_init_ice_9_fports to be called via
  load-extension, and load snarfed things there.  Move open-file
  definition early, to allow ports to bootstrap.
* libguile/ioext.c (scm_init_ice_9_ioext): New function.
  (scm_init_ioext): Similarly, register scm_init_ice_9_ioext as an
  extension.
* libguile/ports.c (scm_set_current_input_port)
  (scm_set_current_output_port, scm_set_current_error_port): Don't
  define Scheme bindings; do that in Scheme.
* libguile/ports.c (scm_i_set_default_port_encoding):
  (scm_i_default_port_encoding, scm_i_default_port_conversion_handler):
  (scm_i_set_default_port_conversion_handler): Since we now init
  encoding early, remove the "init" flags on these encoding/strategy
  vars.
  (scm_init_ice_9_ports): New function.
  (scm_init_ports): Register scm_init_ice_9_ports extension, and define
  some bindings needed by the bootstrap.
* module/Makefile.am (SOURCES): Add ice-9/ports.scm.
* module/ice-9/boot-9.scm: Remove code that's not on the boot path,
  moving it to ice-9/ports.scm.  At the end, load (ice-9 ports).
* module/ice-9/psyntax.scm (include): Use close-port instead of
  close-input-port.
* module/ice-9/psyntax-pp.scm (include): Regenerate.

am/bootstrap.am

@@ -123,6 +123,7 @@ SOURCES =					\
   system/base/ck.scm				\
 						\
   ice-9/boot-9.scm				\
+  ice-9/ports.scm				\
   ice-9/r5rs.scm				\
   ice-9/deprecated.scm				\
   ice-9/binary-ports.scm			\