Adds QueryHandler interface

patch by beobal & slebresne; reviewed by beobal & slebresne for CASSANDRA-6659
Merge branch 'cassandra-2.0' into cassandra-2.1

Conflicts:
	src/java/org/apache/cassandra/cql3/QueryProcessor.java
Allow manually specifying start/end tokens in CFIF
patch by Paulo Gomes; reviewed by Piotr Kołaczkowski for CASSANDRA-6436
merge from 2.0
Restrict Windows to parallel repairs
patch by Josh McKenzie; reviewed by jbellis for CASSANDRA-6907
merge from 2.0