Add descriptive text to nginx conf for GET requests to the verifier

[gene1wood]

The verifier doesn't support GET, only POST. Currently GET requests to the verifier give 404's. Replace this with some kind of descriptive text.

[gene1wood]

Some confusion that inspires this : http://thread.gmane.org/gmane.comp.mozilla.identity.devel/6812

[callahad]

Just changing it to an error 405 instead should be sufficient at this point :)

[fmarier]

I have updated the check_url script: https://github.com/fmarier/checkurl/tree/no_security_improvements

Make sure you use the no_security_improvements branch, not the master branch.