A simple compatability library for *inspector-hook* of CDR-6.
A single symbol *inspector-hook* is exported from the trivial-inspector-hook
package that follows the sematics of CDR-6. This is symbol is also
available via the package nicknames of tih and inspector-hook.
If the current lisp implementation supports CDR-6 then :cdr-6 and
:inspector-hook will be present in *features*.
Recent versions of ABCL, ACL, CCL, CLASP, ECL, Mezzano, and SBCL all support
CDR-6 in some way. If the implemntation exports a symbol with a different
name other than *inspector-hook* then a function is installed the
implementation's hook that calls trivial-inspector-hook:*inspector-hook* if
set.