Avoid assertion in ~AIStateMachine upon viewer exit.

Force the state to bs_killed before clearing the list of statemachines
in AIEngine::flush().

indra/aistatemachine/aistatemachine.cpp

@@ -352,8 +352,13 @@ void AIEngine::mainloop(void)
 
 void AIEngine::flush(void)
 {
-  DoutEntering(dc::statemachine, "AIEngine::flush [" << mName << "]");
   engine_state_type_wat engine_state_w(mEngineState);
+  DoutEntering(dc::statemachine, "AIEngine::flush [" << mName << "]: calling force_killed() on " << engine_state_w->list.size() << " state machines.");
+  for (queued_type::iterator iter = engine_state_w->list.begin(); iter != engine_state_w->list.end(); ++iter)
+  {
+	// To avoid an assertion in ~AIStateMachine.
+	iter->statemachine().force_killed();
+  }
   engine_state_w->list.clear();
 }
 
@@ -906,6 +911,12 @@ void AIStateMachine::callback(void)
   }
 }
 
+void AIStateMachine::force_killed(void)
+{
+  multiplex_state_type_wat state_w(mState);
+  state_w->base_state = bs_killed;
+}
+
 void AIStateMachine::kill(void)
 {
   DoutEntering(dc::statemachine, "AIStateMachine::kill() [" << (void*)this << "]");

indra/aistatemachine/aistatemachine.h

@@ -300,8 +300,9 @@ class AIStateMachine : public LLThreadSafeRefCount
 		mSleep = 0;
 	  return mSleep != 0;
 	}
+	void force_killed(void);												// Called from AIEngine::flush().
 
-	friend class AIEngine;						// Calls multiplex().
+	friend class AIEngine;						// Calls multiplex() and force_killed().
 };
 
 bool AIEngine::QueueElementComp::operator()(QueueElement const& e1, QueueElement const& e2) const