Add parent links to actors.

For each actor, create a context table, with an __index link to the
parent's.  This can be used to propagate information down complex
actor trees.

Code needs to be changed to do AddChild() calls before loading,
rather than after, so context links are available during loads.
This will be done as necessary.

stepmania/src/Actor.cpp

@@ -113,6 +113,17 @@ static bool GetMessageNameFromCommandName( const RString &sCommandName, RString
 Actor::Actor()
 {
 	m_pLuaInstance = new LuaClass;
+	Lua *L = LUA->Get();
+		m_pLuaInstance->PushSelf( L );
+		lua_pushstring( L, "ctx" );
+		lua_newtable( L );
+		lua_pushvalue( L, -1 );
+		lua_setmetatable( L, -2 );
+		lua_settable( L, -3 );
+		lua_pop( L, 1 );
+	LUA->Release( L );
+
+
 	m_size = RageVector2( 1, 1 );
 	InitDefaults();
 	m_bFirstUpdate = true;
@@ -1251,6 +1262,29 @@ void Actor::PlayCommand( const RString &sCommandName, Actor *pParent )
 		RunCommands( *pCmd );
 }
 
+void Actor::PushContext( lua_State *L )
+{
+	// self.ctx should already exist
+	m_pLuaInstance->PushSelf( L );
+	lua_pushstring( L, "ctx" );
+	lua_gettable( L, -2 );
+	lua_replace( L, -2 );
+}
+
+void Actor::SetParent( Actor *pParent )
+{
+	Lua *L = LUA->Get();
+		int iTop = lua_gettop( L );
+
+		this->PushContext( L );
+		lua_pushstring( L, "__index" );
+		pParent->PushContext( L );
+		lua_settable( L, -3 );
+
+		lua_settop( L, iTop );
+	LUA->Release( L );
+}
+
 void Actor::HandleMessage( const RString& sMessage )
 {
 	PlayCommand( sMessage );