Set transaction enabled flag default to TRUE
Merge pull request #2265 from dionysiosarvanitis/fix/trans_enabled

Set transaction enabled flag default to TRUE
Remove CI_DB_pdo_driver::

Improving on PR #2265, the property is inherited with the same value and doesn't need to be set.
Update user_guide_src/source/tutorial/news_section.rst

Clarified a part of the tutorial so it's obvious the code should be replaced/update rather than added.