Ticket #47391 - deleting and adding userpassword fails to update the password

Bug description: Deleting and adding password operation causes
the crash since once an entry is written to and retrieved from
DB, it does not have unhashed#user#password in the entry any
more. The delete userpassword internally invokes delete unhashed
existed in the entry.

Fix description: This patch adds the stricter check for the NULL
reference.

https://fedorahosted.org/389/ticket/47391

Reviewed by Nathan (Thanks!!)
Ticket #47391 - deleting and adding userpassword fails to update the password (additional fix)

Bug description: ldapmodify with changetype "modify" is supposed
to skip checking unhashed password in acl_check_mods.  "delete"
and "replace" were being skipped, but not "add".

Fix description: "add" also skips to check unhashed password.

https://fedorahosted.org/389/ticket/47391

Reviewed by Rich (Thank you!!)
(cherry picked from commit 5337dcfa67827ac46df68a2f817eade638eb352d)