t index
to object index which was previously shadow and now becomes current.
At this moment contents of both indices is synchronized and DyBASE is ready
to start new transaction.<P>

Bitmap of modified object index pages is used to minimize time of committing
transaction. Not the whole object index, but only its modified pages should be
copied. After committing of transaction bitmap is cleared.<P>

When transaction is explicitly aborted by <code>Storage.rollback</code>
method, shadow object index is copied 