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
Added noop compaction strategy
Extracted common logic out of SizeTiered compaction strategy
New compaction strategy to compact by overlappiness.
Fixing bugs
Have to have the background task be synchronized

Needs to be synchronized because it's called multiple times, even on top of
itself.

The reason that instance-level 'synchronized' works is that the lifecycle of
a compaction strategy is one per column-family per cassandra jvm.
Fixing compaction race conditions (NPE on metadata)

I had to only try to compact the ones that weren't currently compacting.
Cutting the number of comparisons down to fib(n - 1)
Renaming overlappiness to avoid overloading 'comparison' as comparable
Trying to improve compaction

Limit the candidates to 90% overlap, and take top 3 pairs.
Got the percentage calculation right finally