Added comments and add explicit ordering to this method, which makes the result…

Added comments and add explicit ordering to this method, which makes the result deterministic and resumeable should an error occur mid-way. 

lib/paperclip.rb

@@ -138,8 +138,10 @@ module Paperclip
       @known_processors[name.to_s] = processor
     end
 
+    # Find all instances of the given Active Record model +klass+ with attachment +name+.
+    # This method is used by the refresh rake tasks.
     def each_instance_with_attachment(klass, name)
-      class_for(klass).all.each do |instance|
+      class_for(klass).find(:all, :order => 'id').each do |instance|
         yield(instance) if instance.send(:"#{name}?")
       end
     end