Use duck typing to also allow MemCache-like object when initializing a MemCacheStore

Signed-off-by: Jeremy Kemper <jeremy@bitsweat.net>

activesupport/CHANGELOG

@@ -1,6 +1,6 @@
 *2.3.3 (pending)*
 
-* Allow MemCacheStore to be initialized with a MemCache object instead of addresses and options [Bryan Helmkamp]
+* Allow MemCacheStore to be initialized with a MemCache-like object instead of addresses and options [Bryan Helmkamp]
 
 
 *2.3.2 [Final] (March 15, 2009)*

activesupport/lib/active_support/cache/mem_cache_store.rb

@@ -39,7 +39,7 @@ module ActiveSupport
       # If no addresses are specified, then MemCacheStore will connect to
       # localhost port 11211 (the default memcached port).
       def initialize(*addresses)
-        if addresses.first.is_a?(MemCache)
+        if addresses.first.respond_to?(:get)
           @data = addresses.first
         else
           @data = self.class.build_mem_cache(*addresses)

activesupport/test/caching_test.rb

@@ -32,6 +32,12 @@ class CacheStoreSettingTest < ActiveSupport::TestCase
     assert_kind_of(ActiveSupport::Cache::MemCacheStore, store)
   end
 
+  def test_mem_cache_fragment_cache_store_with_given_mem_cache_like_object
+    MemCache.expects(:new).never
+    store = ActiveSupport::Cache.lookup_store :mem_cache_store, stub("memcache", :get => true)
+    assert_kind_of(ActiveSupport::Cache::MemCacheStore, store)
+  end
+
   def test_mem_cache_fragment_cache_store_with_multiple_servers
     MemCache.expects(:new).with(%w[localhost 192.168.1.1], {})
     store = ActiveSupport::Cache.lookup_store :mem_cache_store, "localhost", '192.168.1.1'