Changes to RecentChanges plugin. Now takes $limit < 0 to return oldest $limit changes.

Changes to RecentChanges plugin.  Now takes $limit < 0 to return oldest $limit changes.
 $days <=0 is ignored.  So to get the oldest 20 changes in the last three days, use
limit ||= 20, days ||= 3.

git-svn-id: svn://svn.code.sf.net/p/phpwiki/code/trunk@1966 96ab9672-09ca-45d6-a79d-3d69d39ca109