Fix writetime/ttl methods for static columns

patch by slebresne; reviewed by thobbs for CASSANDRA-7081
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	CHANGES.txt
	src/java/org/apache/cassandra/cql3/statements/ColumnGroupMap.java
	src/java/org/apache/cassandra/cql3/statements/SelectStatement.java