Use region specific endpoint for public S3 URLs

[dkocher]

For some regions the URLs https://bucketname.s3.amazonaws.com/key result in a IllegalLocationConstraintException error.

<?xml version="1.0" encoding="UTF-8"?>
--
<Error><Code>IllegalLocationConstraintException</Code><Message>The eu-south-1 location constraint is incompatible for the region specific endpoint this request was sent to.</Message><RequestId>ZAKYSJTFPVJE82FV</RequestId><HostId>1OcnDIrXjw/iUyLeZIfnSbbLeJauSlDRgSrTnCzPBpN4IBNyOqBPDnJF5ABx9CqJRVXV4Oo/PmrsKq5iWXh5V/IWwQe3HaKH</HostId></Error>