Make repair no-op when RF=1

patch by yukim; reviewed by krummas for CASSANDRA-7864
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	src/java/org/apache/cassandra/service/StorageService.java
Merge branch 'cassandra-2.0' into cassandra-2.1.0
Merge branch 'cassandra-2.1.0' into cassandra-2.1
Merge branch 'cassandra-2.1' into trunk