created Cassandra-specific Spring DataAccessException for each Datastax DriverException
aligned C* exceptions more with Spring exceptions than C* ones
DATACASS-34
DATACASS-33 created CompositeRowId for composite primary keys
code cleanup
added tests for nontrivial behavior
Merge branch 'DATACASS-24'
Merge branch 'master' of
https://github.com/shvid/spring-data-cassandra.git into DATACASS-32

Conflicts:
	src/main/java/org/springframework/data/cassandra/config/BeanNames.java
	src/main/java/org/springframework/data/cassandra/core/CassandraTemplate.java