Transfers larger than 2**31 (2147483648) bytes fail

> **2565d84** created the issue

When attempting to download more than 2147483648 bytes (Around 2 GB) Cyberduck gives the following error: 


```
SSH Error:
A badly formatted packet or other SFTP protocol incompatibility was detected.
```

I believe that using an integer type that has a significantly larger capacity (such as a long) for the counter would solve this problem.