SMB file transfers fail complaining of "Not enough credits"

[reapazor]

Occasionally we have builds failing because of an issue with the SMB file transfer of some portion of the build.

Unhandled exception. System.Exception: Not enough credits
   at SMBLibrary.Client.SMB2Client.TrySendCommand(SMB2Command request, Boolean encryptData)
   at SMBLibrary.Client.SMB2FileStore.TrySendCommand(SMB2Command request)
   at SMBLibrary.Client.SMB2FileStore.Disconnect()
   at K9.IO.FileAccessors.SMBFileAccessor.Cleanup()
   at K9.IO.FileAccessors.SMBFileAccessor.GetReader()
   at K9.Setup.Verbs.CopyFile.Execute()
   at K9.Setup.Program.<>c.<Main>b__3_5(CopyFile copy)
   at CommandLine.ParserResultExtensions.MapResult[T1,T2,T3,T4,T5,TResult](ParserResult`1 result, Func`2 parsedFunc1, Func`2 parsedFunc2, Func`2 parsedFunc3, Func`2 parsedFunc4, Func`2 parsedFunc5, Func`2 notParsedFunc)
   at K9.Setup.Program.Main(String[] args)
Process exited with code -532462766

[reapazor]

Some research into this suggested that there may be an issue with the size of the packet reads (not entirely sure on that one), but I also did some work to make sure that stale connections are always cleaned up.

270a11e & c3c1a9e