Don't bounce off disk when putting/gettinging file-like objects

[bitprophet]

Currently, we have to make a temporary file when doing e.g. put(stringio_instance, xxx) or similar.

Paramiko #71 includes a patch that should mean we no longer have to do this. If/when that merges, update to take advantage (and bump our requirements to match...)

Should apply to both put and get.

[bitprophet]

All set.