Fix Edebug's handling of dotted specs (bug#6415)

Fix Edebug's handling of dotted specs (bug#6415)

* lisp/emacs-lisp/cl-macs.el (cl-destructuring-bind): Use
cl-macro-list1 instead of cl-macro-list in Edebug spec.

* lisp/emacs-lisp/edebug.el (edebug-after-dotted-spec): Delete
unused variable.
(edebug-dotted-spec): Add docstring.
(edebug-match-specs): Allow &optional and &rest specs to
match nothing at the tail of a dotted form. Handle matches of
dotted form tails which return non-lists.

* test/lisp/emacs-lisp/edebug-tests.el (edebug-tests-dotted-forms):
New test.

* test/lisp/emacs-lisp/edebug-resources/edebug-test-code.el:
(edebug-test-code-use-destructuring-bind): New function.