Clean up gossiper fully after shadow round.

Patch by brandonwilliams, reviewed by thobbs for CASSANDRA-7318
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	CHANGES.txt
nodetool doesn't error when ~/.cassandra is inaccessible

Patch by Kirk True, reviewed by brandonwilliams for CASSANDRA-6449
Merge branch 'cassandra-2.0' into cassandra-2.1
nodetool doesn't error when ~/.cassandra is inaccessible

Patch by Kirk True, reviewed by brandonwilliams for CASSANDRA-6449