Improved feed aggregation module.

Added support to choose either atom or rss for the "/feed" format.
  Added support for feed format view to feed aggregation.
  Use proper content type for RSS and ATOM response.
  For feed aggregation  use `?view=feed` or `?view=feed.atom` or `?view=feed.rss`
  Improved sized feed view.
  Use site name for recent changes feed title.
  Better name for node feeds (include the site name).
  Use current date when a feed aggregation is converted to a new feed, to set the last build date.
  Fixed category filter per feed location for the feed aggregation module.
Fixed authentication module, where a potential case (but not probable) had no response content.
Cosmetic and minor changes on messaging module.

modules/feed_aggregator/site/files/css/feed_aggregator.css

@@ -1,3 +1,10 @@
+div.feed ul.nav {
+  list-style: none;
+}
+div.feed ul.nav li {
+  display: inline-block;
+  padding-right: 1em;
+}
 div.feed ul {
   list-style: none;
   position: relative;