subselects coding started

OK, I have created the SubLink structure with supporting routines, and
have added code to create the SubLink structures in the parser, and have
added Query->hasSubLink.

I changed gram.y to support:

	(x,y,z) OP (subselect)

where OP is any operator.  Is that right, or are we doing only certain
ones, and of so, do we limit it in the parser?

I still need to add code to handle SubLink fields in the Where clause
and other supporting code, but it should be enough for Vadim to start
coding if he wants to.  I also need to add Var->sublevels_up.

-- 
Bruce Momjian
maillist@candle.pha.pa.us