Fix blank animqueues, and add facing=math.auto to animate

luprex/cpp/core/source.cpp

@@ -765,6 +765,7 @@ LuaNumberConstant(math_pi, M_PI, "");
 LuaNumberConstant(math_huge, HUGE_VAL, "");
 LuaNumberConstant(math_nan, NAN, "");
 LuaNumberConstant(math_maxint, LuaCoreStack::MAXINT, "");
+LuaTokenConstant(math_auto, "auto", "A value used to request that a value should be automatically computed");
 
 // math.random and math.randomseed are in world-accessor.cpp, because
 // generating random numbers must manipulate global state which is