Added tests for reselection events
Updated release notes
Prevented multi-select events from firing if action is a no-op (change in spec)

Previously, selectAll fired a select:all event even if all models had already
been selected beforehand. Similarly, deselectAll fired a select:none event
even if no model had been selected in the first place.

No-ops like this don't trigger an event any more.
Added reselection events