If we're trying to remove an already removed marshaller, let's hear about where we're doing it.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4459 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/presents/server/InvocationManager.java

@@ -146,6 +146,7 @@ public class InvocationManager
         if (_dispatchers.remove(marsh.getInvocationCode()) == null) {
             Log.warning("Requested to remove unregistered marshaller? " +
                         "[marsh=" + marsh + "].");
+            Thread.dumpStack();
         }
     }