- add algorithm detections for old OpenSSH using options -c and -m
  TODO: check this works on OpenSSH 4.6 on msys
- allow MAC algorithm hmac-sha1 for old OpenSSH that don't support any
  of our recommended ones. I'm still not sure this is the right thing to
  do.
- fix detection with 'ssh -Q' that was broken (always skip) by
  ce17097 (release v1.100). The
  impact was our smart detection was ignored and the default list was
  always used. That's not a security issue.

Thanks to this github-keygen now works on OpenSSH 5.1+.

To detect unused variables.

The other cases reported by Test::Vars are false positive.

because Test::Vars is not available on perl 5.8 so this breaks our
Travis-CI build.

Detect bad permissions and fail, with a fix suggestion.
Contrary to pull requests #32, #34 we do not silently fix the issue
because:
- that is not our responsability: if the user did a bad thing he should
  be aware of it and be empowered to fix it.
- to keep user trust doing things silently is forbidden by our policy.