Add beforeChange notification to IEndpointStateChangeSubscriber
Patch by Sergio Bossa, reviewed by brandonwilliams for CASSANDRA-6135
Compact hottest sstables first and optionally omit coldest
patch by Tyler Hobbs; reviewed by jbellis for CASSANDRA-6109
add generation back to bucketing (filtering) sort
update COLD_READS_TO_OMIT_KEY