Implement async_void in alterl bindings

Summary:
  - reply_type for async void functions is now async_void instead of
    the empty struct definition
  - async void functions should return "ok". otherwise the processor
    will crash and the connection will be killed. Is this behaviour
    expected?

Test Plan: tested using testAsync() in ThriftTest. Didn't used to work
           but works now


git-svn-id: https://svn.apache.org/repos/asf/incubator/thrift/trunk@666415 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/lib/alterl/src/thrift_processor.erl b/lib/alterl/src/thrift_processor.erl
index c3434cd..2b435ac 100644
--- a/lib/alterl/src/thrift_processor.erl
+++ b/lib/alterl/src/thrift_processor.erl
@@ -73,7 +73,11 @@
             ok = send_reply(OProto, Function, ?tMessageType_REPLY, Reply);
 
         ok when ReplyType == {struct, []} ->
-            ok = send_reply(OProto, Function, ?tMessageType_REPLY, {ReplyType, {StructName}})
+            ok = send_reply(OProto, Function, ?tMessageType_REPLY, {ReplyType, {StructName}});
+        
+        ok when ReplyType == async_void ->
+            % no reply for async void
+            ok
     end,
     ok.