back-bdb backend_attribute leaks locks with overlays (ITS#3255)

[hyc@OpenLDAP.org]

Full_Name: Howard Chu
Version: HEAD,re22
OS: 
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (24.126.120.178)
Submitted by: hyc


back-bdb's entry_get function compares boi->boi_bdb to op->o_db to see if the
passed in opinfo matches the current backend. But this comparison fails if the
backend has overlays stacked on it, because of all the op->o_db munging going
on. The result is that the wrong lockerID is used to lock the entry, and then
the lock is not released in entry_release.

I'm testing a fix now, that compares be_private pointers.