Stop answering search/geolocate queries from invalid API keys, closes #231.

Also use more realistic test data. The changes to the error message
are ok, as the message part isn't actually specified in the API docs.
It's only the code, domain and reason which are official.
Merge pull request #250 from hannosch/231-disallow-invalid-api-keys

Stop answering search/geolocate queries from invalid API keys, closes #231