https://fedorahosted.org/sssd/ticket/1674

https://fedorahosted.org/sssd/ticket/1673

fixes https://fedorahosted.org/sssd/ticket/1628

When user's alias is same as it's name, don't use it for searching in
sysdb, and for deleting.

https://fedorahosted.org/sssd/ticket/1612

This patch changes the handling of ghost attributes when saving the
actual user entry. Instead of always linking all groups that contained
the ghost attribute with the new user entry, the original member
attributes are now saved in the group object and the user entry is only
linked with its direct parents.

As the member attribute is compared against the originalDN of the user,
if either the originalDN or the originalMember attributes are missing,
the user object is linked with all the groups as a fallback.

The original member attributes are only saved if the LDAP schema
supports nesting.

Using the convenience function instead of low-level ldb calls makes the
code more compact and more readable.

In subdomains we have to use fully qualified usernames.
Unfortunately we have no other good option than simply removing
caches for users of subdomains.
This is because the memberof plugin does not support the rename operation.

The original sysdb code had a strong assumption that only users from one
domain are saved in the databse, with the subdomain feature, we have
changed reality, but have not adjusted all the code arund the sysdb calls
to not rely on the original assumption.

One of the side effects of this incongrunece is that currently group
memberships do not return fully qualified names for subdomain users as they
should.

In oreder to fix this and other potential issues surrounding the violation
of the original assumption, we need to fully qualify subdomain user names.
By savin them fully qualified we do not risk aliasing local users and have
group memberhips or other name based matching code mistake a domain user
with subdomain usr or vice versa.

Add functions to automate setting versions numbers in the db, also
decrease chances of error in copying and pasting code, by setting
the version number only once when we commence the upgrade.

https://fedorahosted.org/sssd/ticket/1589

Added check for determining, whether database version is higher or
lower than expected. To distinguish it from other errors it uses
following retun values (further used for appropriate error message):
EMEDIUMTYPE for lower version than expected
EUCLEAN for higher version than expected

When SSSD or one of it's tools fails on DB version mismatch, new error
message is showed suggesting how to proceed.