Changed database array access to ensure it's always properly setup

This solves my cached entries problem mentioned on issue #137 and probably also its authors problem. I was able to run the phpunit tests under PHP 5.5 with this fix too (it would throw initialization errors and not run with the master branch).

Details:
- Changed $_db access to ensure it's always properly setup
- Fixed typo on comment ('mulitple' -> 'multiple')