Add parse location fields to NullTest and BooleanTest structs.

We did not need a location tag on NullTest or BooleanTest before, because
no error messages referred directly to their locations.  That's planned
to change though, so add these fields in a separate housekeeping commit.

Catversion bump because stored rules may change.

src/backend/parser/parse_expr.c

@@ -789,6 +789,7 @@ transformAExprOp(ParseState *pstate, A_Expr *a)
 		NullTest   *n = makeNode(NullTest);
 
 		n->nulltesttype = IS_NULL;
+		n->location = a->location;
 
 		if (exprIsNullConstant(lexpr))
 			n->arg = (Expr *) rexpr;