warn, then drop queries exceeding a configurable number of tombstones
patch by jbellis; reviewed by slebresne for CASSANDRA-6117
Add configurable metrics reporting
patch by Chris Burroughs; reviewed by Tyler Hobbs for CASSANDRA-4430
Allow alter keyspace on system_traces

patch by yukim; reviewed by jbellis for CASSANDRA-6016
Tracing should log write failure rather than raw exceptions
patch by jbellis; reviewed by ayeschenko for CASSANDRA-6133
merge from 1.2
avoid logging tombstone warnings during compaction
change progressindicator members to CHM
patch by jbellis for CASSANDRA-6129