Adding default on HostKeyCallback

[robermorales]

Since this issue golang/go#19767 the default behaviour of HostKeyCallback changed, so the old behaviour can be achieved with this change.

[kennylevinsen]

Thanks!

Your commit history is a little bit weird, as you're basically making a pull request out of a pull request. I fast-forward merged to avoid a history looking like: "Merge pull request #2: Merge pull request #1: Adding default on HostKeyCallback".

For future reference (not just for this project, but in general), I think it's best to only make pull requests on feature branches. That is, the branch you made a pull request with on your fork should just have been reused to make a pull request towards this upstream repo, rather than using master (which now contained a mege commit). That keeps the git commit history nice and clean.

[robermorales]

Totally agree on the suggestion. Thanks for merging!