Atom readers (Firefox/Liferea) don't like when we embed XHTML anchors

in the description. So adjust the code that creates the changeset
browser title/description to emit a XHTML and plaintext version with
the HTML and Atom output can use, respectively.

Also:

 * Split up @title into @title and @heading as elsewhere
 * Turn the username on the user / user+bbox browser into a link to the userpage
 * Say "Changesets" instead of "Recent changes". Unlike Wikipedia the changes on OSM aren't guaranteed to be recent, they're just going to be the latest

app/views/changeset/list.atom.builder

@@ -5,7 +5,7 @@ atom_feed(:language => I18n.locale, :schema_date => 2009,
   feed.title @title
 
   feed.subtitle :type => 'xhtml' do |xhtml|
-    xhtml.p @description
+    xhtml.p @description_plain
   end
 
   feed.updated @edits.map {|e|  [e.created_at, e.closed_at].max }.max

app/views/changeset/list.html.erb

@@ -1,4 +1,4 @@
-<h1><%= @title %></h1>
+<h1><%= @heading %></h1>
 <p><%= @description %></p>
 
 <%= render :partial => 'changeset_paging_nav' %>