Allow list-valued gcc-self group params.

* gnus-msg.el (gnus-inews-insert-gcc): Allow `gcc-self' to be a list of
groups and t.
* gnus.texi (Group Parameters): Document that `gcc-self' may also be a
list.
Fix a typo.
parse-time.el (parse-time-rules), time-date.el (date-to-time): Don't mishandle year-9999 dates (Bug#18176)
When expiring, tell functions where the articles are going

* gnus-sum.el (gnus-summary-expire-articles): Functions registered to
the gnus-summary-article-expire-hook should be told where the function
is going. In particular, the Gnus registry might want to know.
gnus-sum.el (gnus-summary-expire-articles): Revert last change