Remote port forwarding buffers can grow without limits

[rasantel]

I'm hitting out-of-memory conditions when doing remote port forwarding and the consumer at the end of the tunnel is at times slower than the stream of data coming via ssh.

The buffer for the ChannelInputStream just doubles in size whenever it fills up. I don't see in the implementation any mechanism to slow down the ssh stream.

This is a request to implement such a feature.