[Mysqli] MYSQLI_SERVER_PUBLIC_KEY only exist for php5.5.0 or creater with mysqlnd.
fix composite primary key introspection on Sqlite
Removed comment.
Merge pull request #455 from kimhemsoe/mysqli_mysqlnd_only_constant

[Mysqli] MYSQLI_SERVER_PUBLIC_KEY only exist for php5.5.0 or creater wit...
Merge pull request #457 from deeky666/fix-sqlite-pk-introspection

Fix composite primary key introspection on Sqlite