Redesign reschedule points, allow one operation to reschedule many cpus at once

ce/ce.c

@@ -9,6 +9,7 @@ void app_main (void) {
     char ch;
 
     mail_receive (&ch, 1);
-    mail_send (e_pgid, &ch, 1);
+    test (ch);
+    /* mail_send (e_pgid, &ch, 1); */
   }
 }