Make the 3rd arg optional for #failsafe_response

git-svn-id: http://svn-commit.rubyonrails.org/rails/trunk@3815 5ecf4fe2-1ee6-0310-87b1-e25e094e27de

railties/lib/dispatcher.rb

@@ -85,13 +85,13 @@ def prepare_breakpoint
       end
 
       # If the block raises, send status code as a last-ditch response.
-      def failsafe_response(output, status, exception)
+      def failsafe_response(output, status, exception = nil)
         yield
       rescue Object
         begin
           output.write "Status: #{status}\r\n"
           output.write "Content-Type: text/plain\r\n\r\n"
-          output.write exception.to_s + "\r\n" + exception.backtrace.join("\r\n")
+          output.write exception.to_s + "\r\n" + exception.backtrace.join("\r\n") if exception
         rescue Object
         end
       end