Revision 479089

Added a new org.apache.activemq.kaha.impl.asyc package that holds data manager/journal that implements both the Kaha DataManager and ActiveIO Journal interfaces.
- Initial bench marks show it to be as fast or faster than the default ActiveIO Journal.
- The bigest differentiator is that this implementation of the journal was built to also provide fast reads.
- The DataManager interface was extracted and now the KahaStore can switch between the original DataManager implementation and the new implementation in the kaha.impl.async packagge.
- Simplified the original implementation by removing the AsyncDataWriters stuff since this is largely what the new package is based on.