Improve the Javadoc for Accumulator and implement overflow validation
Modify Accumulator API
Fix various small test failures.  Make SessionId constructor public (miscellaneous).
Fix another test
More Javadoc tweaks
Add the update(long) method back in to ease server changes
Deprecate Tree#getAccumulator
Format
Fix some more Javadoc errors
Remove Tree#getAccumulator
Remove Accumulator#update(long)
merge pbeaman: Improve the Javadoc for com.persistit.Accumulator to provide better information about snapshot and live values, and the semantics of the update method.

https://code.launchpad.net/~pbeaman/akiban-persistit/fix-accumulator-javadoc/+merge/158163