Don't load ActiveRecord during rails initialization

If ThinkingSphinx requires ActiveRecord on load, then setting
configuration in applications' initializers with have no effect (eg
Rails.application.config.active_record.has_many_inversing).

Instead, ActiveRecord should be deferred to the end of initialization
using Railtie

lib/thinking_sphinx.rb

@@ -96,12 +96,15 @@ module Subscribers; end
 require 'thinking_sphinx/utf8'
 require 'thinking_sphinx/wildcard'
 # Extended
-require 'thinking_sphinx/active_record'
 require 'thinking_sphinx/deltas'
 require 'thinking_sphinx/distributed'
 require 'thinking_sphinx/logger'
 require 'thinking_sphinx/real_time'
 
-require 'thinking_sphinx/railtie' if defined?(Rails::Railtie)
+if defined?(Rails::Railtie)
+  require 'thinking_sphinx/railtie'
+else
+  require 'thinking_sphinx/active_record'
+end
 
 ThinkingSphinx.before_index_hooks << ThinkingSphinx::Hooks::GuardPresence

lib/thinking_sphinx/railtie.rb

@@ -7,6 +7,7 @@ class ThinkingSphinx::Railtie < Rails::Railtie
 
   initializer 'thinking_sphinx.initialisation' do
     ActiveSupport.on_load(:active_record) do
+      require 'thinking_sphinx/active_record'
       ActiveRecord::Base.include ThinkingSphinx::ActiveRecord::Base
     end