Support for org.apache.cassandra.db.marshal-namespaced custom types (See #151)

I was unable to get a word from the cassandra developer mailing list (http://www.mail-archive.com/dev@cassandra.apache.org/msg07178.html) so I can't say I am bringing any sort of official functionality. As stated in my issue (#151) instead of seeing the native type over the wire for timestamps, I was seeing this custom type. Seeing how we were unable to continue without a fix in the Go driver I have simply opted to develop this fix.

The issue didn't occur in the official Python driver, so I have opted to duplicate the functionality there (Can be seen @ https://github.com/datastax/python-driver/blob/master/cassandra/cqltypes.py and https://github.com/datastax/python-driver/blob/master/tests/unit/test_types.py).

The first commit fixes what appears to be a type in the `String` function of `TypeInfo`. The next two are the relevant implementations and tests.