Refactor & code cleanup.

Refactor & code cleanup.

Added two new plugin arguments:

  min_age - only display pages which have been "deleted" for at
            least this many days.  (Use min_age=none to get all
            pages, even non-deleted ones listed.)

  max_age - automatically check the checkboxes of pages which
            have been "deleted" this many days or more.

("Deleted" means the current version of the page is empty.
For the most part, PhpWiki treats these "deleted" pages as
if they didn't exist --- but, of course, the PageHistory is
still available, allowing old versions of the page to be restored.)

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@2580 96ab9672-09ca-45d6-a79d-3d69d39ca109