* fixes a number of notices that prevented a feed from being displayed directly in the browser, (or as an aggregated feed via the  {{rss}}  action)
 * some other small bugs fixed as well
 * added @todo and @@@ markers in the source for further issues to be resolved (see #552 a.o); see also remarks about usage of the $item->source attribute (currently used only in an RSS 1.0 feed as a dc:source element)
 * corrects @since tag in recentchanges.xml.php

refs #496,
refs #552