(ITS#8198) pw-pbkdf2: optionally use libnettle for crypto

[luca.bruno@rocket-internet.de]

Full_Name: Luca BRUNO
Version: git:master
OS: Debian
URL: https://github.com/lucab/openldap/commits/lucab/pbkdf2-nettle
Submission from: (NULL) (78.55.218.166)


This is a followup to ITS#7977.
Here below are two patches against the pw-pbkdf2 contrib module to:
 1) fix an always-true check
 2) optionally make use of libnettle

Corresponding patches are available online:
 1) https://github.com/lucab/openldap/commit/f9e42bc1ce85a8c2bc7f3daa06a553b0f79ea6d8.patch
 2) https://github.com/lucab/openldap/commit/b98457fbb009e92d394e0d99851fc720df334db7.patch

Those have been already reviewed by Tsukasa HAMANO:
 * https://github.com/hamano/openldap-pbkdf2/pull/3
 * https://github.com/hamano/openldap-pbkdf2/pull/4

IPR statement follows:

"""
The attached patch is derived from OpenLDAP Software. All of the modifications 
to OpenLDAP Software represented in the following patch(es) were developed by 
Luca BRUNO, on balalf of "Rocket Internet SE". 

By virtue of my employment agreement with "Rocket Internet SE", I have 
assigned my rights and interest in this work to "Rocket Internet SE".

"Rocket Internet AG" has not assigned rights and/or interest in this work to 
any party. I, Luca BRUNO, am authorized by "Rocket Internet SE", my employer, 
to release this work under the following terms.

"Rocket Internet SE" hereby places the following modifications to OpenLDAP 
Software (and only these modifications) into the public domain. Hence, these 
modifications may be freely used and/or redistributed for any purpose with or 
without attribution and/or other notice. 
"""