Refactor: Decouple failed attachments and the flash messages

Attachment#attach_files will no longer need to return a flash message,
instead it will put unsaved attachments into object#unsaved_attachments
where the calling object can access them.

A utility method #render_attachment_warning_if_needed is included for setting
the standard flash warning.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@3528 e93f8b46-1217-0410-a6f0-8f06a7374b81

vendor/plugins/acts_as_attachable/lib/acts_as_attachable.rb

@@ -32,6 +32,8 @@ module Redmine
           has_many :attachments, options.merge(:as => :container,
                                                :order => "#{Attachment.table_name}.created_on",
                                                :dependent => :destroy)
+          attr_accessor :unsaved_attachments
+          after_initialize :initialize_unsaved_attachments
           send :include, Redmine::Acts::Attachable::InstanceMethods
         end
       end
@@ -48,7 +50,11 @@ module Redmine
         def attachments_deletable?(user=User.current)
           user.allowed_to?(self.class.attachable_options[:delete_permission], self.project)
         end
-        
+
+        def initialize_unsaved_attachments
+          @unsaved_attachments ||= []
+        end
+
         module ClassMethods
         end
       end