bugfix: when h was nil (which it was for all my tests), everyone woul…

…d fail with nil.[]= errors. Making sure we at least have a blank hash fixes this.

lib/webrat/rails.rb

@@ -91,6 +91,7 @@ def internal_redirect?
       def follow_redirect_with_headers(h = {})
         raise "Not a redirect! #{@status} #{@status_message}" unless redirect?
 
+        h = Hash.new if h.nil?
         h['HTTP_REFERER'] = request.url
 
         location = headers["location"]