Refactor how driver specific attributes are set

[downsider]

Due to the stupidity of the PDO group, the constant PDO::MYSQL_ATTR_USE_BUFFERED_QUERIES has the same numeric value as the constant PDO::PGSQL_ATTR_DISABLE_NATIVE_PREPARED_STATEMENT. The latter is deprecated in PHP7 and is throwing warnings

A possible solution is to inject an $options array instead of $useBufferedQueries, which contains arrays of options keyed by the DB driver name (mysql, pgsql,etc...). This would allow for attributes to be set only if they were specific to the drivers.
In this solution, we would also need a default key for attributes that are independant of driver (such as PDO::ATTR_TIMEOUT or PDO::ATTR_PERSISTENT)

[dochne]

Note: This error is being thrown on 5.6, so it isn't just a v7 issue.