It should be possible to delete columns by ranges

It is not currently possible to delete a range of columns without retrieving the range through the thrift interface and then deleting the columns by name. An efficient implementation of this is dependent on https://issues.apache.org/jira/browse/CASSANDRA-674, but it can at least be accomplished server-side in the current implementation so as to avoid the overhead of the client-side communication. I'm going to attach one proposed implementation that adds a remove_range_slices api method for parallelism with get_range_slices, but i'm not wedded to either the implementation nor the particular api.