fix merge conflicts in master pom
Catch-all function to set the value of an `AbstractRollupStat`.
bug fix: Variance.toString() should trigger a compute if necessary.
core parts from cd7ada5

TimerRollup extends BasicRollup. This is temporary.
pre-aggregated column family.
Introduce CounterRollup and some tests.
fix openjdk erasure problems.
fix merge conflict
fix merge conflicts in SerializationTest
fix merge conflicts
should have been committed in last batch.
oops. include preaggregation table in truncation list.
Bug Fix: run compute before checking variance equality.
TimerRollup.toString() still reflected that it extended BasicRollup.
fix merge conflicts
 fix merge conflict
Demote `Rollup.java` to an interface.
The rest of the `*Rollup` implementations and rollup operations.

* `CounterRollup`, `GaugeRollup` and `SetRollup` all extend `SingleValueRollup`
* Tests verify rollup semantics
* No rollup tests for `SetRollup` since they will never be rolled up.
CounterRollup, SetRollup, GaugeRollup serialization and tests

* We only serialize a single value for each type
* A single serializer is used for each and uses the type byte to determine what to return.
`Locator.equals` so that locators can work properly in guava collections.