Add paranoid disk failure option.

Patch by marcuse, reviewed by kohlisankalp and jbellis for CASSANDRA-6646
Merge branch 'cassandra-2.0' into cassandra-2.1

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