Set fd initial value to 2s

Patch by brandonwilliams, reviewed by jbellis for CASSANDRA-7307
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/gms/FailureDetector.java
Merge branch 'cassandra-2.0' into cassandra-2.1