fixes zeromq#829

fixes zeromq#829 issue with NetMqMonitor

Author: amichel

src/NetMQ/ISocketPollableCollection.cs

@@ -1,3 +1,4 @@
+using System;
 using JetBrains.Annotations;
 using NetMQ.Monitoring;
 
@@ -13,5 +14,6 @@ public interface ISocketPollableCollection
     {
         void Add([NotNull] ISocketPollable socket);
         void Remove([NotNull] ISocketPollable socket);
+        void RemoveAndDispose<T>(T socket) where T : ISocketPollable, IDisposable;
     }
 }

src/NetMQ/Monitoring/NetMQMonitor.cs

@@ -24,7 +24,7 @@ public class NetMQMonitor : IDisposable
     {
         [NotNull] private readonly NetMQSocket m_monitoringSocket;
         private readonly bool m_ownsMonitoringSocket;
-        [CanBeNull] private NetMQPoller m_attachedPoller;
+        [CanBeNull] private ISocketPollableCollection m_attachedPoller;
         private int m_cancel;
 
         private readonly ManualResetEvent m_isStoppedEvent = new ManualResetEvent(true);
@@ -216,7 +216,7 @@ private void InternalClose()
             }
         }
 
-        public void AttachToPoller([NotNull] NetMQPoller poller)
+        public void AttachToPoller<T>(T poller) where T : ISocketPollableCollection
         {
             if (poller == null)
                 throw new ArgumentNullException(nameof(poller));