Fixing rebalancing issues caused by:

1) missing old node remove when moving branch
2) does not taking into account that the first node of branch page can have empty key during node size calculation
Merge pull request #5 from arekais/voron

Fixing rebalancing issues caused by:
Fixing tests failing in release mode
Small refactoring - introducing interface so we can change free space policies more easily
Adding trivial implementation for no free space utilization
Returning to current free space repository
added TreeWriter for WriteBatch
Merge branch 'voron' of https://github.com/ayende/raven.voron into voron
Adding unmanaged bits impl
support writing to multiple trees in single batch
Merge branch 'voron' of github.com:ayende/raven.voron into voron
Build fix
Made the ItemsCount test more comprehensive and removed an erroneous assignment of ItemCount in the TreeRebalancer.