Describes how to compact the database.
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 compacting 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.