Consider the following snippet in `~/.ssh/config`:

	 Host foo
	 HostKeyAlias bar

for a host which is *not* participating in the monkeysphere.

For such a host, when using `monkeysphere-ssh-proxy-command`, the
public keyservers will be queried on each attempted ssh connection
(even after a successful connection).

This appears to be because:

* `ssh` itself will write a line to `~/.ssh/known_hosts`, but it will
  be labeled with `bar` because of the `HostKeyAlias`. 

* `monkeysphere` won't be able to find any mention of it in the
  keyring (it's not in the monkeysphere)

* `monkeysphere-ssh-proxycommand` won't be able to find it in the
  `known_hosts` file because it looks for `foo`, which is never
  matched.

excessive keyserver querying is bad behavior, because it causes delays
for the users, and puts excessive load on the public keyserver
infrastructure.

How can we resolve this?