Small performance improvement for Rails 3, but not as satisfying as t…

…aking the conditions and joins from the original scope and applying them to a new scope. Haven't found out how to do that in Rails 3.0 yet :(

lib/acts_as_taggable_on/acts_as_taggable_on/collection.rb

@@ -115,7 +115,9 @@ def all_tag_counts(options = {})
         if ActiveRecord::VERSION::MAJOR >= 3
           # Append the current scope to the scope, because we can't use scope(:find) in RoR 3.0 anymore:
           scoped_select = "#{table_name}.#{primary_key}"
-          tagging_scope = tagging_scope.where("#{ActsAsTaggableOn::Tagging.table_name}.taggable_id IN(#{select(scoped_select).to_sql})").
+          scoped_sql    = select(scoped_select).to_sql
+
+          tagging_scope = tagging_scope.joins("JOIN (#{scoped_sql}) AS conditional_join ON conditional_join.#{primary_key} = #{ActsAsTaggableOn::Tagging.table_name}.taggable_id").
                                         group(group_columns).
                                         having(having)
         else