* Added log4net dependency to physxplugin in prebuild.xml.
* Added missing m_log fields to classes.
* Replaced Console.WriteLine with appropriate m_log.Xxxx
* Tested that nant test target runs succesfully.
* Tested that local opensim sandbox starts up without errors.
* Created value object for EstateRegionLink for storing the estate region relationship.
* Refactored slightly NHibernateManager and NHibernateXXXXData implementations for accesing nhibernate generated ID on insert.
** Changed NHibernateManager.Save method name to Insert as it does Insert.
** Changed NHibernateManager.Save return value object as ID can be both UUID and uint currently.
** Changed NHibernateManager.Load method Id parameter to object as it can be both UUID and uint.
* Created NHibernateEstateData implementation. This is the actual estate storage.
* Created NHibernate mapping files for both EstateSettings and EstateRegionLink
* Created MigrationSyntaxDifferences.txt files to write notes about differences in migration scripts between different databases.
* Created estate storage migration scripts for all four databases.
* Created estate unit test classes for all four databases.
* Updated one missing field to BasicEstateTest.cs
* Tested NHibernate unit tests with NUnit GUI. Asset databases fail but that is not related to this patch.
* Tested build with both Visual Studio and nant.
* Executed build tests with nant succesfully.
