[SSSD] [sssd PR#413][opened] mmap_cache: add SID and type to struct sss_mc_rec

[sumit-bose]

URL: https://github.com/SSSD/sssd/pull/413
Author: sumit-bose
 Title: #413: mmap_cache: add SID and type to struct sss_mc_rec
Action: opened

PR body:
"""
This patchset updates the memory cache by adding some new members to struct
sss_mc_rec. One is the addition of a hash value for SID based lookup which will
be added in later patches.

The other is a new record type and a member indicating the type. The new type
is a link record which links an alias name, e.g. an UPN, to the original record
of the related user or group object.

Besides aliases this link record will be used in case in-sensitive setups. E.g.
if getpwnam() returns the name of an AD users as [e-mail] bit
some applications or users use [e-mail] for lookups the memory
cache is currently never used because there is no entry with the hash of
'[e-mail]'. With this patch the original data record is created
as before with the hash for '[e-mail]' and a link record is
create with the hash of '[e-mail]'. Now both lookups can be
handled by the memory cache. If now another application uses
[e-mail] for lookups the first request will go to the NSS
responder but upcoming requests can use the memory cache as well because a link
record for [e-mail] is created.

The last patch in this series adds some additional data to the user and group
lookup requests, the short name, the domain name, the short domain name and the
SID. Those are needed to be able to support SID based lookups in the memory
cache and allow applications to not depend on the name format returned by
getpw{nam|uid}. Upcoming patches for libsss_nss_idmap will make those
additional values available to applications I added them already here to keep
the memory cache related changes in one PR. Application which will benefit here
are the interfaces SSSD provides e.g. to Samba related applications like SSSD's
version of libwbclient but also IPA plugins like extdom and slapi-nis.
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/413/head:pr413
git checkout pr413