Logs from confdb with missing '\n' in the DEBUG statements annoyed me so
I decided to fix them. I also made a quick grep through the code and
found other places so I fixed them too.

Implements a different mechanism for cleanup task. Instead of just
deleting expired entries, this patch adds a new option
account_cache_expiration for domains. If an entry is expired and the last
login was more days in the past that account_cache_expiration, the entry is
deleted.

Groups are deleted if they are expired and and no user references them
(no user has memberof: attribute pointing at that group).

The parameter account_cache_expiration is not LDAP-specific, so that other
future backends might use the same timeout setting.

Fixes: #391

This reverts commit 75a9f18ad8ac6e885ac34cdeebc4d8f8734713f8.

Adds a new option that tells resolver which address family to prefer or
use exclusively.

Fixes: #404

Kerberos-specific options are pulled using dp_get_opts() and defined
in Kerberos subtree. There is no need to keep these in confdb.

Also update BUILD.txt