Modify set rollups to track individual items seen instead of counters.

This is done by hashing each object as it observed, and storing the hashes.  hashes are then merged on rollup.

This puts SetRollup in the same class as TimerRollup in that full-resolution stores rollup objects rather than primitives.
Merge branch 'master' into set_rollups_v2
use getHashes() instead of accessing hash directly.
update changes
Merge pull request #203 from gdusbabek/set_rollups_v2

Set rollups v2 - track individual items across rollups (up to 24h)