Add "anonymous" namespaces.

* cl-ns.el ([namespace] cl): Use anoymous feature for testing.

* namespace-test.el (test-h.7, test-h.8): Neww tests

* namespace.el ([struct] namespace): New slot prefix.
(namespace--find-or-make-namespace): Initializes it.
(namespace--validate-unique): Anomymous namespeces have nil as
name.
(namespace--sexp-namespace-p) : New
(namespace--parse-namespace, namespace--sexp-import-set-p)
(namespace--parse-import-set): Accept new syntax.
(namespace--make-anonymous-namespace)
(namespace--create-namespace): New helpers.
(namespace--set-imports): Use it.
(namespace--qsym-to-csym): Use prefix slot.
Add :re-export syntax.

* cl-ns.el ([namespace] cl): Use :re-export syntax.

* namespace.el (namespace--parse-options)
(namespace--parse-import-set, namespace--set-exports)
(namespace--define, define-namespace): Support re-exports.
(namespace--create-import-sets): New helper.
(namespace--set-imports): Use it.
* Makefile: Minor cleanups.
Use nadvice instead of the semi-deprecated defadvice.

* namespace-tools.el (search-for-symbol-advice)
(function-called-at-point-advice, eval-sexp-add-defvars-advice)
(pp-last-sexp-advice, lisp-indent-function-advice, advice*)
(deactivate): New helpers.
(activate): Use them