Align bucket naming rules with S3 2006-03-01 API rules.

Permit bucket names that follow the less restrictive naming rules specified in
http://docs.aws.amazon.com/AmazonS3/2006-03-01/dev/BucketRestrictions.html
but restrict dns compatible names to the more restrictive rules in the same document.
Add mixed case bucket name test scenario.
Merge pull request #220 from attili/master

Align bucket naming rules with S3 2006-03-01 API rules.