captures for "when" statements

update Triggers to IntrusivePtr's and simpler AST traversal
introduce IDSet type, migrate associated "ID*" types to "const ID*"

src/script_opt/ZAM/Stmt.cc

@@ -1115,7 +1115,7 @@ const ZAMStmt ZAMCompiler::CompileWhen(const WhenStmt* ws)
 		z.v1 = is_return;
 		}
 
-	z.e = cond;
+	z.e = cond.get();
 
 	auto when_eval = AddInst(z);