Improving various checks by Heikki Linnakangas <heikki@enterprisedb.com>

- add code to check that the query tree is well-formed. It was indeed
  possible to send malformed queries in binary mode, which produced all
  kinds of strange results.

- make the left-field a uint32. There's no reason to
  arbitrarily limit it to 16-bits, and it won't increase the disk/memory
  footprint either now that QueryOperator and QueryOperand are separate
  structs.

- add check_stack_depth() call to all recursive functions I found.
  Some of them might have a natural limit so that you can't force
  arbitrarily deep recursions, but check_stack_depth() is cheap enough
  that seems best to just stick it into anything that might be a problem.

src/backend/utils/adt/tsrank.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/tsrank.c,v 1.2 2007/09/07 15:09:56 teodor Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/tsrank.c,v 1.3 2007/09/07 15:35:10 teodor Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -508,6 +508,10 @@ Cover(DocRepresentation *doc, int len, TSQuery query, Extention *ext)
 	int			i;
 	bool		found = false;
 
+	/* since this function recurses, it could be driven to stack overflow.
+	 * (though any decent compiler will optimize away the tail-recursion.   */
+	check_stack_depth();
+
 	reset_istrue_flag(query);
 
 	ext->p = 0x7fffffff;