Print the faulty object upon invalid-keyword errors.
* libguile/vm.c (vm_error_kwargs_invalid_keyword,
vm_error_kwargs_unrecognized_keyword): Add parameter. Pass it
enclosed in a list as the last argument to `scm_error_scm'.
* libguile/vm-i-system.c (bind_kwargs): Adjust accordingly.
* libguile/eval.c (error_invalid_keyword, error_unrecognized_keyword):
Add parameter.
(prepare_boot_closure_env_for_apply): Adjust accordingly.
* module/ice-9/eval.scm (primitive-eval): Likewise.
* libguile/error.c (scm_error_scm): Mention `keyword-argument-error' in
docstring.
* module/ice-9/boot-9.scm (keyword-error-printer): New procedure; use it.
* test-suite/tests/optargs.test (c&e, with-test-prefix/c&e): Remove.
("define*")["unrecognized keyword"]: Test the value passed along the
`keyword-argument-error' exception.
["invalid keyword"]: New test.
* doc/ref/api-control.texi (Error Reporting): Update `scm-error'
description.