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
Remove CHANGES.txt dups
Make MS.getBoundTerms() correct for batched statements

patch by Aleksey Yeschenko and Sam Tunnicliffe; reviewed by
Sylvain Lebresne
Fixes for compacting larger-than-memory rows
patch by jbellis; reviewed by marcuse for CASSANDRA-6274
Remove multithreaded compaction and PCR
patch by jbellis; reviewed by marcuse for CASSANDRA-6142
Merge branch 'cassandra-2.0' into trunk
merge from 2.0