Call to socket.getfqdn takes quite a lot of time on systems that don't have a fully qualified domain name. This patch makes the call happen only when it is explicitly required. On my systems the speed difference is very significant.
Compute host's FQDN on demand only
Changelog re #128
Document SSHConfig FQDN logic.
Merged with pre-picked changes re #128.
Merged this with #110, thanks!
Thanks for merging!