Apply changes from GNU ELPA

Apply changes from GNU ELPA

* doc/yas-doc-helper.el:
* yasnippet-debug.el:
* yasnippet-tests.el: Fix up copyright headers.

* yasnippet-tests.el: Fix lexical-binding cookie.
* yasnippet-debug.el: Require cl.

* yasnippet-tests.el: Silence byte-compiler.
(yas-saving-variables, yas-with-snippet-dirs): Move macros before their use.
(yas--barbaz, yas--foobarbaz): Declare.
(yas--phony-c-mode, yas--test-mode, yas--another-test-mode): Move out of
deftest, so the byte-compiler understands they're defined.