Stop using method missing for singleton delegation.

This saved about 46 array allocations per request on an extremely simple
application.  The delegation happened in the notification subsystem
which is a hotspot, so this should result in even more savings with
larger apps.

Squashed commit of the following:

commit 41eef0d1479526f7de25fd4391d98e61c126d9f5
Author: Aaron Patterson <aaron.patterson@gmail.com>
Date:   Wed Nov 6 16:32:31 2013 -0800

    speed up notifications

commit 586b4a18656f66fb2c518fb8e8fee66a016e8ae6
Author: Aaron Patterson <aaron.patterson@gmail.com>
Date:   Wed Nov 6 16:31:05 2013 -0800

    speed up runtime registry methods

commit b67d074cb4314df9a88438f785868cef77e583d7
Author: Aaron Patterson <aaron.patterson@gmail.com>
Date:   Wed Nov 6 16:28:12 2013 -0800

    change method name and make it public

5 files changed, 15 insertions, 9 deletions

diff --git a/activerecord/lib/active_record/runtime_registry.rb b/activerecord/lib/active_record/runtime_registry.rb
index 63e6738622..9d605b826a 100644
--- a/activerecord/lib/active_record/runtime_registry.rb
+++ b/activerecord/lib/active_record/runtime_registry.rb
@@ -13,5 +13,10 @@ module ActiveRecord
     extend ActiveSupport::PerThreadRegistry
 
     attr_accessor :connection_handler, :sql_runtime, :connection_id
+
+    [:connection_handler, :sql_runtime, :connection_id].each do |val|
+      class_eval %{ def self.#{val}; instance.#{val}; end }, __FILE__, __LINE__
+      class_eval %{ def self.#{val}=(x); instance.#{val}=x; end }, __FILE__, __LINE__
+    end
   end
 end
diff --git a/activesupport/lib/active_support/cache/strategy/local_cache.rb b/activesupport/lib/active_support/cache/strategy/local_cache.rb
index fb42c4a41e..cea7eee924 100644
--- a/activesupport/lib/active_support/cache/strategy/local_cache.rb
+++ b/activesupport/lib/active_support/cache/strategy/local_cache.rb
@@ -23,6 +23,9 @@ module ActiveSupport
           def set_cache_for(local_cache_key, value)
             @registry[local_cache_key] = value
           end
+
+          def self.set_cache_for(l, v); instance.set_cache_for l, v; end
+          def self.cache_for(l); instance.cache_for l; end
         end
 
         # Simple memory backed cache. This cache is not thread safe and is intended only
diff --git a/activesupport/lib/active_support/notifications.rb b/activesupport/lib/active_support/notifications.rb
index b32aa75e59..7a96c66626 100644
--- a/activesupport/lib/active_support/notifications.rb
+++ b/activesupport/lib/active_support/notifications.rb
@@ -178,7 +178,7 @@ module ActiveSupport
       end
 
       def instrumenter
-        InstrumentationRegistry.instrumenter_for(notifier)
+        InstrumentationRegistry.instance.instrumenter_for(notifier)
       end
     end
 
diff --git a/activesupport/lib/active_support/per_thread_registry.rb b/activesupport/lib/active_support/per_thread_registry.rb
index aa682fb36c..a5e7389d16 100644
--- a/activesupport/lib/active_support/per_thread_registry.rb
+++ b/activesupport/lib/active_support/per_thread_registry.rb
@@ -32,21 +32,19 @@ module ActiveSupport
   #
   # If the class has an initializer, it must accept no arguments.
   module PerThreadRegistry
+    def instance
+      Thread.current[name] ||= new
+    end
+
     protected
 
       def method_missing(name, *args, &block) # :nodoc:
         # Caches the method definition as a singleton method of the receiver.
         define_singleton_method(name) do |*a, &b|
-          per_thread_registry_instance.public_send(name, *a, &b)
+          instance.public_send(name, *a, &b)
         end
 
         send(name, *args, &block)
       end
-
-    private
-
-      def per_thread_registry_instance
-        Thread.current[name] ||= new
-      end
   end
 end
diff --git a/activesupport/lib/active_support/subscriber.rb b/activesupport/lib/active_support/subscriber.rb
index f2966f23fc..4b9b48539f 100644
--- a/activesupport/lib/active_support/subscriber.rb
+++ b/activesupport/lib/active_support/subscriber.rb
@@ -94,7 +94,7 @@ module ActiveSupport
     private
 
       def event_stack
-        SubscriberQueueRegistry.get_queue(@queue_key)
+        SubscriberQueueRegistry.instance.get_queue(@queue_key)
       end
   end