title: SphinxQL support for inner join on the same index with subquery
body: <p>I wish to do inner join a the same index in SphinxQL</p>
  
  <pre>
  select * from my_index w inner join 
  (select test_id,max(val1) from my_index where match('xxxx') group by test_id) as w2 
  on w.test_id=w2.test_id and w.val1=w2.val1;
  </pre>
  
  <p>but it's getting syntax error.</p>
  
  <p>my sphinxServer Server version is 2.0.6-id64-release. what's wrong?  does Sphinx or SphinxQL support inner join on with subquery?</p>