Fix unintended update with conditional statement

patch by slebresne; reviewed by iamaleksey for CASSANDRA-6893
Replace equals by type compare
Don't shut ExpiringMap down.

Patch by Benedict, reviewed by brandonwilliams for CASSANDRA-6948
Fix collection element access in IF

patch by slebresne; reviewed by thobbs for CASSANDRA-6914
Handle short slice start/finishes of different lengths

Patch by Tyler Hobbs; reviewed by Sylvain Lebresne as a follow-up for
CASSANDRA-6825