Add TODO item, check soa serial first when doing zone refreshment.

git-svn-id: svn://bind10.isc.org/svn/bind10/trunk@2905 e5f2f494-b856-4b98-b285-d166d9295462

src/bin/xfrin/TODO

@@ -64,4 +64,5 @@
     this approach each thread needs to watch at least two channels,
     and then it would need some asynchronous communication mechanism.
 17. Do zone transfer from notifyfrom address first, if it's one master of the zone.
+18. Check soa serial first when doing zone refreshment.