correct exception for WaitForConfirms

Same reasoning as for the Java client: if the underlying channel
closed, we throw and AlreadyClosedException; if we received a nack, we
die with an IOException.

Author: Alexandru Scvortov

projects/client/RabbitMQ.Client/src/client/impl/ModelBase.cs

@@ -938,7 +938,7 @@ public bool WaitForConfirms()
             lock (m_unconfirmedSet.SyncRoot) {
                 while (true) {
                     if (CloseReason != null)
-                        throw new OperationInterruptedException(CloseReason);
+                        throw new AlreadyClosedException(CloseReason);
 
                     if (m_unconfirmedSet.Count == 0) {
                         bool aux = m_onlyAcksReceived;
@@ -957,7 +957,7 @@ public void WaitForConfirmsOrDie()
                                             CommonFraming.Constants.ReplySuccess,
                                             "Nacks Received", new IOException("nack received")),
                       false);
-                throw new OperationInterruptedException(CloseReason);
+                throw new IOException("Nacks Received");
             }
         }