Reset @html_document between requests so assert_tag works. Closes #4810.

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@4591 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

actionpack/CHANGELOG

 *SVN*
 
+* Reset @html_document between requests so assert_tag works. #4810 [jarkko@jlaine.net, easleydp@gmail.com]
+
 * Update render :partial documentation. #5646 [matt@mattmargolis.net]
 
 * Integration tests behave well with render_component. #4632 [edward.frederick@revolution.com, dev.rubyonrails@maxdunn.com]

actionpack/lib/action_controller/integration.rb

@@ -250,6 +250,8 @@ def process(method, path, parameters=nil, headers=nil)
           # tests.
           @response.extend(TestResponseBehavior)
 
+          @html_document = nil
+
           parse_result
           return status
         end