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
Improve nodetool cleanup/scrub/upgradesstables failure handling.

Patch by marcuse, reviewed by jbellis for CASSANDRA-6774
Improve PerRowSecondaryIndex performance

patch by Sergio Bossa; reviewed by Aleksey Yeschenko for CASSANDRA-6876
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/db/Keyspace.java
	src/java/org/apache/cassandra/db/index/SecondaryIndexManager.java
Add support for DELETE ... IF EXISTS to CQL3

Patch by Tyler Hobbs, reviewed by Sylvain Lebresne for CASSANDRA-5708
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/cql3/statements/ModificationStatement.java
Extend triggers to support CAS updates

patch by Sam Tunnicliffe; reviewed by Aleksey Yeschenko for
CASSANDRA-6882
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/triggers/TriggerExecutor.java
	test/unit/org/apache/cassandra/triggers/TriggersTest.java
Pick unused generations when loading new sstables

patch by Tyler Hobbs; reviewed by Jonathan Ellis for CASSANDRA-6514
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/db/ColumnFamilyStore.java
Ninja-commit to suppress blist-related warnings in cqlsh
Include correct consistencyLevel in LWT timeout
patch by Sankalp Kohli; reviewed by jbellis for CASSANDRA-6884
merge from 2.0
Merge remote-tracking branch 'origin/cassandra-2.1' into cassandra-2.1
Omit tombstones from schema digests
patch by Oleg Anastasyev; reviewed by jbellis for CASSANDRA-6862
merge from 2.0
Static columns with IF NOT EXISTS don't always work as expected

patch by slebresne; reviewed by iamaleksey for CASSANDRA-6783
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/cql3/statements/ModificationStatement.java
Extend limits.conf in debian packaging.

Patch by brandonwilliams for CASSANDRA-6104