src/module-parse.lisp (read-module): Use requested pathname for location.

src/module-parse.lisp (read-module): Use requested pathname for location.

The default behaviour for `charbuf-scanner' is to use the pathname from
its underlying stream; but (at least on some implementations) this is an
absolute pathname which is actually rather annoying in error messages.

Instead, arrange for `read-module' to attach the namestring of the
pathname it was given directly to the scanner.  This will be the correct
possibly-relative pathname to the module file, because `find-file' has
already done that part of the work, but it will be relative if that's
how it was specified on the command line, if it was found by merging
with a relative pathname in the `*module-dirs*' list, or if it was
imported by a name relative to a module with a relative pathname.