Updated PDO driver requirement to use boolean

Scrutinizer picks up on this as a minor bug. I.e. count($drivers) returns an integer rather than a boolean.
minor #110 Updated PDO driver requirement to use boolean (elliot)

This PR was merged into the 2.3.x-dev branch.

Discussion
----------

Updated PDO driver requirement to use boolean

Scrutinizer picks up on this as a minor bug. I.e. count($drivers) returns an integer rather than a boolean.

Commits
-------

7c03132 Updated PDO driver requirement to use boolean