https://fedorahosted.org/389/ticket/47808
https://fedorahosted.org/389/attachment/ticket/47808/0001-Ticket-47808-If...
Bug description: Backend add ldbm_back_add frees the entry to be added,
if the add fails in the be_txn plugins. But the frontend releases the
entry when an error is returned from the backend.
Fix desxription: When the entry is freed in the backend, set NULL to
the pblock SLAPI_ADD_ENTRY to tell the frontend not to free the entry.