Changed aggregate to ignore UseCursor when talking with a pre-2.6 server.

Author: craiggwilson

src/MongoDB.Driver.Core.Tests/Core/Operations/AggregateOperationTests.cs

@@ -143,8 +143,7 @@ public void CreateCommand_should_create_the_correct_command(
                 { "maxTimeMS", () => maxTime.Value, maxTime.HasValue }
             };
 
-            var defaultCursorValue = semanticServerVersion >= new SemanticVersion(2, 6, 0);
-            if (useCursor.GetValueOrDefault(defaultCursorValue))
+            if (semanticServerVersion >= new SemanticVersion(2, 6, 0) && useCursor.GetValueOrDefault(true))
             {
                 expectedResult["cursor"] = new BsonDocument
                 {

src/MongoDB.Driver.Core/Core/Operations/AggregateOperation.cs

@@ -200,8 +200,7 @@ internal BsonDocument CreateCommand(SemanticVersion serverVersion)
                 { "maxTimeMS", () => _maxTime.Value.TotalMilliseconds, _maxTime.HasValue }
             };
 
-            var defaultCursorValue = serverVersion >= __version26;
-            if (_useCursor.GetValueOrDefault(defaultCursorValue))
+            if (serverVersion >= __version26 && _useCursor.GetValueOrDefault(true))
             {
                 command["cursor"] = new BsonDocument
                 {
@@ -213,7 +212,7 @@ internal BsonDocument CreateCommand(SemanticVersion serverVersion)
 
         private AsyncCursor<TResult> CreateCursor(IChannelSourceHandle channelSource, BsonDocument command, AggregateResult result)
         {
-            if (_useCursor.GetValueOrDefault(true))
+            if (channelSource.ServerDescription.Version >= __version26 && _useCursor.GetValueOrDefault(true))
             {
                 return CreateCursorFromCursorResult(channelSource, command, result);
             }