[SSSD] [PATCHES] simple access provider: support subdomain users and groups

[Pavel Březina]

Patch 0001:
I haven't used this one after all, but I still think it is nice to have. 
It reduces amount of code duplication.

Patch 0005:
> /* Try to get group SID and assign it a domain */
> group_sid = ldb_msg_find_attr_as_string(group, SYSDB_SID_STR, NULL);
> if (group_sid == NULL) {

I'm not sure if this branch isn't a dead code, but I kept it there 
because it mimics current behaviour.
>    /* We will look it up in main domain. */
>    domain = state->ctx->domain;
> } else {
>    domain = find_subdomain_by_sid(state->ctx->domain, group_sid);
>    if (domain == NULL) {
>        DEBUG(SSSDBG_CRIT_FAILURE, ("There is no domain information for "
>                                    "SID %s\n", group_sid));
>        return ENOENT;
>    }
> }