BabuDB:

- added support for automatic database conversions if the database format changes
- made parameters such as the number of entries per mini page and the maximum size of an on-disk index file configurable
- fixed a bug that could cause start-up failures if indices existed without on-disk index files
- refactoring: moved configuration classes to org.xtreemfs.babudb.config

git-svn-id: https://babudb.googlecode.com/svn/trunk@204 d4c7dd96-b7b2-11dd-893d-d98698f66bbf