Remove ability to change num_tokens once set.

Patch by brandonwilliams, reviewed by thobbs for CASSANDRA-7649
Merge branch 'cassandra-2.0' into cassandra-2.1.0

Conflicts:
	src/java/org/apache/cassandra/service/StorageService.java
Ninja: remove buggy test assertion from 2.1

This was fixed by CASSANDRA-7390, but that fix starts with Cassandra
3.0.
Fix typo in v3 native protocol spec

Patch by Robert Stupp; review by Tyler Hobbs for CASSANDRA-7652