Database compaction

When a File-store database is constructed using the RDbNamedDatabase interface, there is no access to the underlying store in order to compact it and recover any free space for re-use.

The RDbDatabase abstract base class, however, supports a compaction interface, the Compact() member function. The class also offers a complementary interface, the UpdateStats() and Size() member functions, which calculate and report size and usage information.

Incremental forms of these functions are also offered by the RDbIncremental class.