Added the following signature:

* Retrieve all user objects with given filestore for a given context.
* If filestore_id is null all user objects with a own filestore for a given context are retrieved instead.
* @param context
* Context object.
* @param auth
* Credentials for authenticating against server.
* @return User[] with currently ONLY id set in each User.
* @throws RemoteException
* General RMI Exception
* @throws StorageException
* When an error in the subsystems occured.
* @throws InvalidCredentialsException
* When the supplied credentials were not correct or invalid.
* @throws NoSuchContextException
* If the context does not exist in the system.
* @throws InvalidDataException
* If the data sent within the method contained invalid data.
* @throws DatabaseUpdateException
public User[] listUsersWithOwnFilestore(final Context context, final Credentials auth, final Integer filestore_id) throws RemoteException, StorageException, InvalidCredentialsException, NoSuchContextException, InvalidDataException, DatabaseUpdateException;