checker: require unsafe for free()

examples/sokol/particles/particles.v

@@ -47,7 +47,9 @@ fn (mut a App) init() {
 }
 
 fn (mut a App) cleanup() {
-	a.ps.free()
+	unsafe {
+		a.ps.free()
+	}
 }
 
 fn (mut a App) run() {

examples/tcp_echo_server.v

@@ -26,7 +26,9 @@ fn handle_client(mut socket net.TcpConn) {
 	eprintln('> new client: $client_addr')
 	mut reader := io.new_buffered_reader(reader: socket)
 	defer {
-		reader.free()
+		unsafe {
+			reader.free()
+		}
 	}
 	socket.write_string('server: hello\n') or { return }
 	for {

examples/term.ui/pong.v

@@ -470,7 +470,9 @@ fn frame(x voidptr) {
 
 fn cleanup(x voidptr) {
 	mut app := &App(x)
-	app.free()
+	unsafe {
+		app.free()
+	}
 }
 
 fn fail(error string) {