[#432][#403][#433][#422] Fix checking for column cache until db connects

Specifically see,
https://github.com/mbleigh/acts-as-taggable-on/issues/432#issuecomment-30769459
Merge pull request #438 from bf4/fix_cached_tag_columns_check

[#432][#403][#433][#422] Fix checking for column cache until db connects