Techedit/database

Technical edits for testing-db.markdown file.

One thing that I couldn't test was the custom array dataset code, as PHPUnit_Util_Filter::addFileToFilter(__FILE__, 'PHPUNIT'); no longer exists in PHPUnit and I'm not sure what the exact replacement is. I found what should be replacement code for directory filters, but not file filters. This seems to have changed after PHPUnit 3.4.