Improved FileGroupMgr support - for creating and deleting file groups.
This implementation is not yet complete.
Fix DB upgrade script to support transition from schema 400 to 401.
Added support to FileGroupMgr for adding paths into a source file group.
Refactored the FileGroupMgr API so that the method names are more
consistent with their purpose.
Add support for generated file group, including transient entries.
Add support for merge file groups.
Add support for querying file groups by package.