support dynamic-composties when retrieving column families

There were two problems.

1) (.getClassName comparator-type) can return something like:
`org.apache.cassandra.db.marshal.DynamicCompositeType(t=>org.apache.cassandra.db.marshal.TimeUUIDType,s=>org.apache.cassandra.db.marshal.UTF8Type)` so the map lookup in `types` fails.

2) :comparator-alias was not handled at all