Added ability to write to a non-readonly slave

StackExchange.Redis/StackExchange/Redis/IServer.cs

@@ -37,6 +37,11 @@ public partial interface IServer : IRedis
         /// </summary>
         bool IsSlave { get; }
 
+        /// <summary>
+        /// Explicitly opt in for slave writes on writable slaves
+        /// </summary>
+        bool AllowSlaveWrites { get; set; }
+
         /// <summary>
         /// Gets the operating mode of the connected server
         /// </summary>

StackExchange.Redis/StackExchange/Redis/PhysicalBridge.cs

@@ -770,7 +770,7 @@ private bool WriteMessageToServer(PhysicalConnection connection, Message message
             {
                 var cmd = message.Command;
                 bool isMasterOnly = message.IsMasterOnly();
-                if (isMasterOnly && serverEndPoint.IsSlave)
+                if (isMasterOnly && serverEndPoint.IsSlave && (serverEndPoint.SlaveReadOnly || !serverEndPoint.AllowSlaveWrites))
                 {
                     throw ExceptionFactory.MasterOnly(multiplexer.IncludeDetailInExceptions, message.Command, message, ServerEndPoint);
                 }

StackExchange.Redis/StackExchange/Redis/RedisServer.cs

@@ -37,6 +37,12 @@ public RedisFeatures Features
 
         public bool IsSlave { get { return server.IsSlave; } }
 
+        public bool AllowSlaveWrites
+        {
+            get { return server.AllowSlaveWrites; }
+            set { server.AllowSlaveWrites = value; }
+        }
+
         public ServerType ServerType { get { return server.ServerType; } }
 
         public Version Version { get { return server.Version; } }

StackExchange.Redis/StackExchange/Redis/ServerEndPoint.cs

@@ -114,6 +114,8 @@ public long OperationCount
 
         public bool SlaveReadOnly { get { return slaveReadOnly; } set { SetConfig(ref slaveReadOnly, value); } }
 
+        public bool AllowSlaveWrites { get; set; }
+
         public Version Version { get { return version; } set { SetConfig(ref version, value); } }
 
         public int WriteEverySeconds { get { return writeEverySeconds; } set { SetConfig(ref writeEverySeconds, value); } }