Fix bug with PDO::FETCH_COLUMN fetch mode

This fixes a big with PDO::FETCH_COLUMN fetch mode where the value
was not returned.
Add support for PDO::ATTR_DRIVER_NAME

Adds support for PDO::ATTR_DRIVER_NAME to getAttribute(). This call
returns "oci" for the driver beings used by PDO. By implementing this
method libraries using this PDO driver will know which driver is being
used and accurately use an Oracle dialect.