Fix millisecond timestamps in Tracing

patch by Aleksey Yeschenko; reviewed by Sam Tunnicliffe for
CASSANDRA-8297
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/tracing/Tracing.java
Merge branch 'cassandra-2.1' into trunk

Conflicts:
	src/java/org/apache/cassandra/config/CFMetaData.java
	src/java/org/apache/cassandra/tracing/TraceState.java
	src/java/org/apache/cassandra/tracing/Tracing.java