### Please describe the problem.
Openssh was not compiled to support ed25519 algorithm

### What steps will reproduce the problem?
only enable ed25519 on server and try to connect via ssh.
fails with "no hostkey alg"

### What version of git-annex are you using? On what operating system?
5.20150219-gd24cfd3, Android 5.0.1

regards,
David
