Minor changes

tests/task_handling.py

@@ -11,7 +11,9 @@ async def main_cancel(i):
         print(f"[main] Child spawned, waiting {i} seconds before canceling it")
         await structio.sleep(i)
         print("[main] Cancelling child")
-        # Tasks can be cancelled individually, if necessary
+        # Tasks can be cancelled individually, if necessary.
+        # Cancellation is not a checkpoint, by the way (as
+        # evidenced by the lack of the 'await' keyword!)
         task.cancel()
     print(f"[main] Exited in {structio.clock() - t:.2f} seconds")