Stop threads that are no longer in use.

Author: tosh-coding

src/AsyncFiberWorks/Procedures/SequentialHandlerWaiter.cs

@@ -166,6 +166,7 @@ public void Dispose()
                 _notifierExecutionRequested.Dispose();
                 _notifierExecutionFinished.Dispose();
             }
+            _thread.Dispose();
         }
     }
 }

src/AsyncFiberWorks/Procedures/SequentialTaskWaiter.cs

@@ -156,6 +156,7 @@ public void Dispose()
                 _notifierExecutionRequested.Dispose();
                 _notifierExecutionFinished.Dispose();
             }
+            _thread.Dispose();
         }
     }
 }