Don't require storage module files directly.

lib/paperclip.rb

@@ -37,6 +37,7 @@ require 'paperclip/thumbnail'
 require 'paperclip/interpolations'
 require 'paperclip/style'
 require 'paperclip/attachment'
+require 'paperclip/storage'
 require 'paperclip/callback_compatability'
 require 'paperclip/command_line'
 require 'paperclip/railtie'

lib/paperclip/attachment.rb

@@ -275,13 +275,11 @@ module Paperclip
 
     def initialize_storage #:nodoc:
       storage_class_name = @storage.to_s.capitalize
-      storage_file_name = @storage.to_s.downcase
       begin
-        require "paperclip/storage/#{storage_file_name}"
-      rescue MissingSourceFile
-        raise StorageMethodNotFound, "Cannot load 'paperclip/storage/#{storage_file_name}'"
+        @storage_module = Paperclip::Storage.const_get(storage_class_name)
+      rescue NameError
+        raise StorageMethodNotFound, "Cannot load storage module '#{storage_class_name}'"
       end
-      @storage_module = Paperclip::Storage.const_get(storage_class_name)
       self.extend(@storage_module)
     end
 

lib/paperclip/storage.rb

+require "paperclip/storage/filesystem"
+require "paperclip/storage/s3"