boto.DynamoDB2 support

[xtsimpouris]

• Numerous changes to support boto.DynamoDB2, and its new method query_2
• Hash keys can now be anything and not just latin, they are packaged through hashlib
• A pop dict-like function
• DynamoDB2 supports save by comparison, so some code can be safely deleted (still haven't fully tested yet)
• getitem in Dynamo object now supports also a tuple, in case you want to specify on the fly the base Table class. This became a need when I wanted to create pro grammatically create DynamoDB tables