* doc/ref/posix.texi (Ports and File Descriptors): Document new
  interfaces.
* libguile/filesys.c (scm_close, scm_close_fdes)
* libguile/fports.c (fport_close):
* libguile/ioext.c (scm_primitive_move_to_fdes): Call
  scm_run_fdes_finalizers.
* module/ice-9/fdes-finalizers.scm:
* test-suite/tests/fdes-finalizers.test:
* libguile/fdes-finalizers.h:
* libguile/fdes-finalizers.c: New files.
* module/Makefile.am:
* test-suite/Makefile.am:
* libguile/Makefile.am:
* libguile.h:
* libguile/init.c: Wire up new files.