2.26.100: checkpointing a lot of progress.
* Pathname support has been cleaned up, yet again, extending and renaming COERCE-PATHNAME into PARSE-UNIX-NAMESTRING, also ENSURE-PATHNAME, many docstrings, and plenty of small enhancements. * Bundles were refactored to take advantage of the new, more sensible, component-depends-on semantics. * Image support was cleaned up again, and program-op was implemented to produce a standalone executable on supported platforms; a working hello-world-example is included amongst tests. * The *compile-file-function* indirection was removed, with the ECL and MKCL object file support being folded into compile-file* instead. * systems now can have NIL as component-pathname, instead of providing a non-sensible bogus pathname when no sensible pathname was determined. Most of our pathname functions have sensible default behavior when provided NIL instead of a pathname as an argument.