Merge pull request mbleigh#403 from shekibobo/fix-heroku-precompile

Check to see if we can connect to the db before accessing it. Fixes mbleigh#396.

lib/acts_as_taggable_on/acts_as_taggable_on/cache.rb

@@ -2,7 +2,7 @@ module ActsAsTaggableOn::Taggable
   module Cache
     def self.included(base)
       # Skip adding caching capabilities if table not exists or no cache columns exist
-      return unless base.table_exists? && base.tag_types.any? { |context| base.column_names.include?("cached_#{context.to_s.singularize}_list") }
+      return unless base.connected? && base.table_exists? && base.tag_types.any? { |context| base.column_names.include?("cached_#{context.to_s.singularize}_list") }
 
       base.send :include, ActsAsTaggableOn::Taggable::Cache::InstanceMethods
       base.extend ActsAsTaggableOn::Taggable::Cache::ClassMethods