Add custom secondary index support to CQL3

patch by Aleksey Yeschenko; reviewed by Sylvain Lebresne for
CASSANDRA-5484
Merge branch 'cassandra-1.2' into trunk

Conflicts:
	NEWS.txt
	doc/cql3/CQL.textile
	src/java/org/apache/cassandra/cql3/Cql.g
	src/java/org/apache/cassandra/cql3/QueryProcessor.java
	src/java/org/apache/cassandra/cql3/statements/CreateIndexStatement.java