Improve Gossip tolerance of abnormally slow tasks
patch by jbellis; reviewed by jasobrown for CASSANDRA-6338
Merge branch 'cassandra-2.0' into trunk
Fix paging with reversed slices

patch by slebresne; reviewed by iamalesksey for CASSANDRA-6343
Merge branch 'cassandra-2.0' into trunk
Set minTimestamp correctly to be able to drop expired sstables correctly

patch by marcuse, reviewed by jbellis for CASSANDRA-6337
Merge branch 'cassandra-2.0' into trunk