Kahadb does not allow to obtain count of used/free bytes in the storage

The full story is user forum under title:
Activemq 5.4.2 hangs when the temp disk usage is used

TempUsage.retrieveUsage() always returns the size of the allocated storage instead of the actual usage. I could not see what methods of kahadb returns the needed information, so I extended the kahadb interface.

Note that this issue may cause other problems such as AMQ-4136.