Fix default value for 'attribute_set_id'.

[colinmollenhour]

The variable "$row" is passed to _getTableRecord, but since $row is a copy of $value[$index] it was not receiving the default attribute_set_id.

[colinmollenhour]

Added another commit for cases where I specify a table in a fixture with no rows which is useful for just truncating tables that were updated during the test to avoid foreign key errors.

[colinmollenhour]

Thanks for the merge, and for the great PHPUnit module!