Ticket #48188 - segfault in ns-slapd due to accessing Slapi_DN freed in pre bind plug-in
Description: Additional fixes based upon the comments by firstname.lastname@example.org
(Thank you, Rich!!).
1. Implemented the case 2)
If the plugin changes the SLAPI_BIND_TARGET_SDN *value*,
we need to select a different backend. It is possible
(but not very useful) for the plugin to change the pointer,
but use the same value.
2. Added an api slapi_be_select_exact which returns NULL if
there is no matching backend.
Reviewed by email@example.com (Thank you!)
(cherry picked from commit 8212a8913b748cd1f5e986a754c37ef41db8272a)