Rendering a template from ActionView will default to looking for partials only in the current mime type.

* The old behavior was tested only as a side-effect of a different test--the original tests remain;
    a new template in the XML mime was added.
  * If you are relying on the current behavior and object to this change, please participate in
    http://groups.google.com/group/rubyonrails-core/browse_thread/thread/6ef25f3c108389bd

actionpack/lib/action_view/base.rb

@@ -248,7 +248,7 @@ module ActionView #:nodoc:
     def with_template(current_template)
       _evaluate_assigns_and_ivars
       last_template, self.template = template, current_template
-      last_formats, self.formats = formats, [current_template.mime_type.to_sym] + Mime::SET.symbols
+      last_formats, self.formats = formats, current_template.formats
       yield
     ensure
       self.template, self.formats = last_template, last_formats

actionpack/lib/action_view/template/text.rb

@@ -15,7 +15,9 @@ module ActionView #:nodoc:
     def render(*) self end
     
     def mime_type() @content_type end
-      
+
+    def formats() [mime_type] end
+
     def partial?() false end
   end
 end

actionpack/test/fixtures/test/greeting.xml.erb

@@ -0,0 +1 @@
+<p>This is grand!</p>