Fix skipping memcache tests if a memcache server isn't running

actionpack/test/dispatch/session/mem_cache_store_test.rb

@@ -32,6 +32,10 @@ def rescue_action(e) raise end
   end
 
   begin
+    require 'memcache'
+    memcache = MemCache.new('localhost:11211')
+    memcache.set('ping', '')
+
     def test_setting_and_getting_session_value
       with_test_route_set do
         get '/set_session_value'