Validate CF existence on execution for prepared statement

patch by aholmber; reviewed by slebresne for CASSANDRA-6535
Merge branch 'cassandra-1.2' into cassandra-2.0

Conflicts:
	src/java/org/apache/cassandra/service/ClientState.java
Merge branch 'cassandra-2.0' into trunk
Use Atomic*FieldUpdater to save memory.

Patch by marcuse, reviewed by belliottsmith for CASSANDRA-6281.
cql3注释
Merge branch 'trunk' of http://git-wip-us.apache.org/repos/asf/cassandra into trunk