Address a few RSS and Atom feed validation problems:

Address a few RSS and Atom feed validation problems:
  * Make OPAC URLs absolute (needs refinement to respect locale/skin)
  * Push datetime creation down to the feed and item level
  * Atom:
    * Merge summary fields into a single element
  * RSS2:
    * Generate a channel/description field
    * Merge item/description fields into a single element
    * Use RFC-822 dates (adds DateTime::Format::Mail as a prerequisite)
    * Set guid isPermaLink attribute false as we're using tag: URIs
    * Place alternate link elements in the xhtml namespace
    * Generate a link element with no attributes

git-svn-id: svn://svn.open-ils.org/ILS/trunk@9950 dcc99617-32d9-48b4-a31d-7c20da2025e4