Allow pid file to be read by mere mortals.

Patch by Michael Shuler, reviewed by brandonwilliams for CASSANDRA-7851
Merge branch 'cassandra-2.0' into cassandra-2.1
Fix yaml snitch reconnect trick

Patch by Holger Bornträger, reviewed by brandonwilliams for CASSANDRA-7912
Merge branch 'cassandra-2.0' into cassandra-2.1
deprecate yaml snitch
Fix CHANGES.txt
Dont try to set repairedAt on old sstables

Patch by marcuse; reviewed by jbellis for CASSANDRA-7913
Add human readable option to nodetool outputs.

Patch by Michael Nelson, reviewed by brandonwilliams for CASSANDRA-5433
Don't try to shutdown client servers if they don't exist.

Patch by Steve Nelson, reviewed by brandonwilliams for CASSANDRA-7889
Merge branch 'cassandra-2.0' into cassandra-2.1
CASSANDRA-7507 - OOM killer cherry-picked
Reorder enum to be consistent with config file
Added doc for new options
Added 'die' logic to existing failure detection points
Added unit tests for JVMStabilityInspector
Added unit tests for new die logic (that was tested elsewhere)