back to the current index, eliminating
all changes done by aborted transaction. After the end of copying,
both indices are identical again and database state corresponds to the moment
before the start of current transaction.<P>

Allocation of object handles is done by free handles list. Header of the list
is also shadowed and two instances of list headers are stored in database
header. Switch between them is done in the same way as switch of
object indices. When there are no more free elements in the list, 