add history for manual hostnames entered

```
It would be nice to have a history for non-saved sessions entered using a 'ssh 
username@hostname' format so they could be easily pulled back up.

We should ensure that history could be deleted and that a real putty session 
with the same name overrides the history.
```

Original issue reported on code.google.com by `matthew....@gmail.com` on 28 Feb 2011 at 9:13
