Routine Description:

    This routine is used to apply the changes of a registry sub-tree
    Transaction to that registry sub-tree.  This routine is meant to be
    called for the common case, where the hive is automatically
    lazy-flushed.  That means that this routine must write the change log
    to disk, then flush the hive (to ensure that pieces of changes aren't
    lazy-written to disk before this routine finishes an atomic operation),
    the apply the changes, then delete the change log.

    The actual changes will be lazy-written to disk, but the registry
    guarantees that none or all will make it.  If the machine goes down
    while this routine is executing, the flushed change log guarantees
    that the hive can be put into a consistent state.


    RXactContext - Supplies a pointer to the RXactContext structure for this
        subsystem's root registry key.

Return Value:

    STATUS_SUCCESS - Indicates the transaction was completed.

    STATUS_UNKNOWN_REVISION - Indicates that a transaction state
        exists for the specified sub-tree, but has a revision level that is
        unknown by this service.

    STATUS_RXACT_INVALID_STATE - Indicates that the transaction state
        of the registry sub-tree is incompatible with the requested operation.
        For example, a request to start a new transaction while one is already
        in progress, or a request to apply a transaction when one is not
        currently in progress.  This may also indicate that there is no
        transaction state at all for the specified registry sub-tree.