Fixes #41, Blocking: Process can leak in Self Play

Two issues addressed in this change.  1) while waiting for the engine
response (which can be on the order of seconds/minutes worst case)
we also wait on the exit event now, in case it comes during that time.
2) The Dispose path for the UCIChessEngine class was just wrong.  At
some point the code diverged and I forgot to clean it up.  Thanks to
stockfish being so damned resilient, I missed it until now.  It's why
testing is important.

AllPawnsMustDie/core/UCIChessEngine.cs

@@ -97,6 +97,9 @@ public void Dispose()
             {
                 // Stop listening to stdout of engine process
                 engineProcess.OutputDataReceived -= OnDataReceived;
+                // Send the UCI quit if we haven't
+                ((IChessEngine)this).Quit();
+
                 // Dispose of the process
                 engineProcess.Dispose();
                 disposed = true;
@@ -357,8 +360,13 @@ public void CommandQueueExecutionMethod()
                             engineProcess.StandardInput.WriteLine(IsReady);
                         }
 
-                        // Wait for the response
-                        uciCommandFinished.WaitOne();
+                        // Wait on the exit event as well, so we can bail as fast as needed
+                        AutoResetEvent[] commandEvents = { uciCommandFinished, shutdownCommandQueue };
+                        int commandWait = WaitHandle.WaitAny(commandEvents);
+                        if (commandWait == 1)
+                        {
+                            exitThread = true;
+                        }
                     }
                 }
             }
@@ -373,10 +381,7 @@ void IChessEngine.Quit()
             // engine will exit ASAP, so assume it's gone after this
             if (engineProcess != null && !(Disposed))
             {
-                // Unsubscribe from the handler as this will close the process
-                //engineProcess.OutputDataReceived -= OnDataReceived;
                 engineProcess.StandardInput.WriteLine(UciQuit);
-                Dispose();
             }
         }
         #endregion