Fix issue with 1.6 compiler
Add test for testing code path where we insert proposed items out of order
Fix parent pointer in invoice tree node
Fix issue in rebalance
Initial unit tests for NodeInterval class
NEWS: prepare for release

Signed-off-by: Pierre-Alexandre Meyer <pierre@ning.com>
[maven-release-plugin] prepare release killbill-0.8.13
[maven-release-plugin] prepare for next development iteration
Code review integration
- Introduce tree walker
- Fix item adjustement ordering problem
- Rework ItemsInterval
Revert walkChildren method introduced in NodeInterval
Rework the NodeInterval class to abstract the custom logic and leave that class very generic.
Add unit tests for NodeInterval
NodeInterval and other invoice tree related classes rework; in particular:
- Fix search apis and add unit tests
- Add method to walk the tree and build json serialization on top of it.
- Other renaming
Minor edit for code review integration of invoice tree code
Invoice fix to address issues related with leading pro-rations.

In the case of billingPeriod different than MONTHLy the current code would do an initial leading pro-ration to the billCycleDate within
the current or next months. Those would cause different issues as documented in #57, #146 and #160.

The new logic will compute the longest leading pro-ration and as a side effect will address those issues.

Fixes #57, Fixes #146, Fixes #160
Fix a bug in calculation of firstBillingCycleDay.

Add unit tests of that method to verify through various case scenarios that it computes the right date.
Merge remote-tracking branch 'origin/master' into new-amount-decimals-handling-rfc
Merge remote-tracking branch 'origin/invoice2' into new-amount-decimals-handling-rfc

Signed-off-by: Pierre-Alexandre Meyer <pierre@mouraf.org>

Conflicts:
	beatrix/src/test/java/com/ning/billing/beatrix/integration/TestSubscription.java
	invoice/src/test/java/com/ning/billing/invoice/TestInvoiceHelper.java
	invoice/src/test/java/com/ning/billing/invoice/tests/inAdvance/annual/TestProRation.java
	invoice/src/test/java/com/ning/billing/invoice/tests/inAdvance/quarterly/TestProRation.java