Inconsistent server/client configuration

[Hans Werner Strube]

It appears somewhat inconsistent to me that parameter HostKey is configurable
on the server side but fixed on the client side.
On the client, always _PATH_HOST_KEY_FILE, _PATH_HOST_DSA_KEY_FILE,
_PATH_HOST_RSA_KEY_FILE are used (in this order), whereas on the server,
the paths can be specified by up to three HostKey options as arbitrary names
in arbitrary sequence.
Similarly, option GlobalKnownHostsFile is configurable for the client only
but fixed as _PATH_SSH_SYSTEM_HOSTFILE for the server. (Well, here the meaning
is slightly different, thus this may be o.k.)