Revert "Don't shut ExpiringMap down."

This reverts commit d4ec31f21eb83502bd523c057bce2d3b249b3d80.

Conflicts:
	CHANGES.txt
Handle short slice start/finishes of different lengths

Patch by Tyler Hobbs; reviewed by Sylvain Lebresne as a follow-up for
CASSANDRA-6825
Skip range calculations for range slices on LocalStrategy keyspaces

Patch by Tyler Hobbs; reviewed by Jonathan Ellis for CASSANDRA-6906