Added a ping program.

modules/net/ping.lua

@@ -0,0 +1,13 @@
+s("pingd",function()
+ while true do
+  if ev[1] == "net_msg" then
+   if ev[3] == "ping" then
+    print("ping ("..ev[2].."): "..ev[4])
+    ns(ev[2],"pong",ev[4])
+   elseif ev[3] == "pong" then
+    print("pong ("..ev[2].."): "..ev[4])
+   end
+  end
+  C.yield()
+ end
+end)