Paginator_Basic: fix for DSQL data source

Reported here: https://groups.google.com/forum/?fromgroups=#!topic/agile-toolkit-devel/0ZfjkoCXpIY

Contains:
1) fix for DSQL data source
2) slightly simplify setSource() and recursiveRender() methods

// Test case
$q=$this->api->db->dsql();
$q->table('building')->field('name');
$g = $this->add('Grid');
$g->addColumn('text','name');
$g->makeSortable();
$g->setSource($q);
$g->addPaginator(1);