* 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.