Add `rake initializer`

This task prints out initializers for an application. It is useful to
develop a rubygem which involves the initialization process.

railties/CHANGELOG.md

+*   Add `rake initializer`
+
+    This task prints out initializers for an application. It is useful to
+    develop a rubygem which involves the initialization process.
+
+    *Naoto Kaneko*
+
 *   Created rake restart task. Restarts your Rails app by touching the 
     `tmp/restart.txt`.
 

railties/lib/rails/tasks.rb

@@ -4,6 +4,7 @@
 %w(
   annotations
   framework
+  initializer
   log
   middleware
   misc

railties/lib/rails/tasks/initializer.rake

+desc "Prints out initializers for your application"
+task initializer: :environment do
+  Rails.application.initializers.tsort_each do |initializer|
+    puts initializer.name
+  end
+end