HEADS UP: slapd: struct entry change

["Kurt D. Zeilenga" <Kurt@OpenLDAP.org>]

Slapd's struct entry has been modified to allow per backend type
private information (using the new void* e_private field).

The LDBM specific fields have been moved into a new struct
(ldbm_entry_info) hanging off the e_private pointer.  The new
structure is managed by and only to the LDBM cache.

As part of this change, entry lock management has been
moved from the frontend to the backend.  This allows each
to provide the required locking in their own way.  LDBM
continues to use r/w locks, however, they are now managed
by it's cache.

Ksp will be updating the experimental BDB2 backend to use
locking features of Berkeley DB2.

Kurt