Fix watchdog timer hanging on exit (r=dvander).

sourcepawn/jit/engine2.cpp

@@ -192,6 +192,7 @@ bool SourcePawnEngine2::Initialize()
 
 void SourcePawnEngine2::Shutdown()
 {
+	g_WatchdogTimer.Shutdown();
 	g_Jit.ShutdownJIT();
 }
 

sourcepawn/jit/watchdog_timer.cpp

@@ -31,7 +31,7 @@ WatchdogTimer::WatchdogTimer()
 
 WatchdogTimer::~WatchdogTimer()
 {
-  Shutdown();
+  assert(!thread_);
 }
 
 bool