3.0.1.6: have other traverse variants not call plan-actions, either
3.0.1.7: tweaks for XCVB: better support CFASL on SBCL, default-encoding.
3.0.1.8: trivial refactoring of format in function die.
3.0.1.9: better OS detection for MCL and ABCL. Restore MCL support.

Thanks to Chun Tian (binghe) for his feedback.
MCL has issues with make-pathname failing to override defaults with an explicit NIL component.