Minor regression in SphinxQL documentId alias

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What steps will reproduce the problem?

  SELECT id AS id FROM my_index

Other variants w/o AS, with backquoted alias, alias in different case result in 
the same error. However if alias is different from case-insensitive "id" the 
query works.

What is the expected output? What do you see instead?

  ERROR 1064 (42000): sphinxql: syntax error, unexpected ID, expecting IDENT near 'id from my_index'

What version of the product are you using? On what operating system?

"2.0.4-1.1ubuntu1 (raring)" worked correctly. Current stable 
"2.1.3-release-1~wheezy" has the regression. The bug can be related to 
http://sphinxsearch.com/bugs/view.php?id=1264.

Also note that such alias can make no sense for hand-written queries it can be 
produces by a SQL generation utility.

Original issue reported on code.google.com by i...@saaj.me on 15 Nov 2013 at 3:23