CQL3: improve support for paginating over composites

patch by slebresne; reviewed by iamaleksey for CASSANDRA-4851
Fix count(*) queries in a mixed cluster

patch by Tyler Hobbs; reviewed by Piotr Kołaczkowski for CASSANDRA-6707
Merge branch 'cassandra-2.0' into trunk

Conflicts:
	src/java/org/apache/cassandra/cql3/CFDefinition.java
	src/java/org/apache/cassandra/cql3/ColumnNameBuilder.java
	src/java/org/apache/cassandra/cql3/Cql.g
	src/java/org/apache/cassandra/cql3/statements/SelectStatement.java
	src/java/org/apache/cassandra/db/marshal/CompositeType.java
Undo CASSANDRA-6707 from trunk