* libguile/ports.c (scm_init_ports): Export the port fluids to Scheme,
temporarily.
* module/ice-9/boot-9.scm (fluid->parameter): Turn `current-input-port'
et al into srfi-39 parameters, backed by the exported fluids, then
remove the fluids from the guile module.
(%cond-expand-features): Add srfi-39.
* module/srfi/srfi-39.scm: Re-export features from boot-9.
* test-suite/tests/parameters.test: Add tests.
* module/ice-9/boot-9.scm (<parameter>, make-parameter, parameter?)
(parameter-fluid, parameter-converter, parameterize): New top-level
bindings, implementing SRFI-39 parameters. Currently,
current-input-port and similar procedures are not yet parameters.
* test-suite/Makefile.am:
* test-suite/tests/parameters.test: Add tests, taken from srfi-39
tests.
