Kohana_Config_Database should extend Config_Database_Writer

`Kohana_Config_Database` should extend `Config_Database_Writer`
but not `Kohana_Config_Database_Writer`.

This is to ensure that changes to Config_Database_Writer affect
Kohana_Config_Database when transparently extending through
the Kohana CFS.
Merge pull request #85 from kohana/3.3/bugfix/config_database_writer-cfs-extension

Kohana_Config_Database should extend Config_Database_Writer