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/tsquery_rewrite.c

@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/tsquery_rewrite.c,v 1.2 2007/09/07 15:09:56 teodor Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/tsquery_rewrite.c,v 1.3 2007/09/07 15:35:10 teodor Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -22,6 +22,9 @@
 static int
 addone(int *counters, int last, int total)
 {
+	/* since this function recurses, it could be driven to stack overflow. */
+	check_stack_depth();
+
 	counters[last]++;
 	if (counters[last] >= total)
 	{
@@ -173,6 +176,9 @@ findeq(QTNode *node, QTNode *ex, QTNode *subs, bool *isfind)
 static QTNode *
 dofindsubquery(QTNode *root, QTNode *ex, QTNode *subs, bool *isfind)
 {
+	/* since this function recurses, it could be driven to stack overflow. */
+	check_stack_depth();
+
 	root = findeq(root, ex, subs, isfind);
 
 	if (root && (root->flags & QTN_NOCHANGE) == 0 && root->valnode->type == QI_OPR)