make sim use proper OOP

sim/gate.lua

@@ -38,18 +38,22 @@ function Gate.getportisrising(self, index)
 	return Port.isrising(self.ports[index])
 end
 
-function Gate:getportisfalling(index)
+function Gate.getportisfalling(self, index)
 	return Port.isfalling(self.ports[index])
 end
 
 function Gate.cb(gate, ...)
-	Simulation.queuecallback(gate.sim, gate, ...)
+	Simulation.queuecallback(Gate.getsim(gate), gate, ...)
 end
 
-function Gate.queue(self, delay)
-	Simulation.queuegatelater(self.sim, self, delay)
+function Gate.queue(gate, delay)
+	Simulation.queuegatelater(Gate.getsim(gate), gate, delay)
 end
 
 function Gate.gettick(gate)
-	return gate.sim.currenttick
+	return Gate.getsim(gate).currenttick
+end
+
+function Gate.getsim(gate)
+	return gate.sim
 end