Add support for PDO::ATTR_DRIVER_NAME

Adds support for PDO::ATTR_DRIVER_NAME in getAttribute(). This call
returns "oci" for the driver beings used by PDO. By implementing this
method libraries using this attribute to know which driver is being
used will accurately know to use Oracle dialect.
Fix bug with PDO::FETCH_COLUMN fetch mode

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