Added mutex locking to to FtpClient.Dispose() to allow other threads to complete a transaction before disposing.
Added mutex locking to to FtpClient.Dispose() to allow other threads to complete a transaction before disposing.

worstenbrood/FluentFTP,kendallb/System.Net.FtpClient,robinrodricks/FluentFTP,robinrodricks/FluentFTP,hgupta9/FluentFTP,shaneray/ShaneSpace.FtpClient,robinrodricks/FluentFTP,shaneray/ShaneSpace.FtpClient