adding sentinel command

Author: pbeardshear

src/ServiceStack.Redis/Commands.cs

@@ -180,5 +180,8 @@ public static class Commands
         public readonly static byte[] Px = "PX".ToUtf8Bytes();
         public readonly static byte[] Nx = "NX".ToUtf8Bytes();
         public readonly static byte[] Xx = "XX".ToUtf8Bytes();
+
+		// Sentinel commands
+		public readonly static byte[] Sentinel = "SENTINEL".ToUtf8Bytes();
     }
 }

src/ServiceStack.Redis/RedisNativeClient.cs

@@ -1209,6 +1209,24 @@ public byte[] BRPopLPush(string fromListId, string toListId, int timeOutSecs)
             return result.Length == 0 ? null : result[1];
         }
 
+		public object[] Sentinel(string command, string master = null)
+		{
+			if (command == null)
+				throw new ArgumentNullException("command");
+
+			var args = new List<byte[]>()
+			{
+				Commands.Sentinel,
+				command.ToUtf8Bytes()
+			};
+
+			if (master != null)
+			{
+				args.Add(master.ToUtf8Bytes());
+			}
+			return SendExpectDeeplyNestedMultiData(args.ToArray());
+		}
+
         #endregion