bug fix for #15 implementing a different calling method with the S3 API

On close inspection, I was able to track down the problem. With the new S3 API, you are likely to have problems connecting via HTTPS to your buckets if your bucket names have periods (.) in them. In order to fix this, I changed from using the default calling format of "SubdomainCallingFormat" to using the "OrdinaryCallingFormat"[1](https://github.com/boto/boto/issues/421). This also has the side effect of creating/using buckets in the US region by default. In order to compensate, I've added a new environment parameter called the KEYCHAIN_BUCKET_LOCATION which will contain the region that your bucket is/should be located.