[pkg] fix paths in debian doc-base control file

[ldapfeed] extid and cwuri aren't the same thing Historically, we used a ldap://... URI as cwuri attribute, not just the dn. The extid field, OTOH, was always the dn. So when initializing our dict of known entities from an ldap source, look at existing extids, not cwuris, to avoid importing already-existing users (and violated unicity constraints).

[entities] add eid to ISerializableAdapter Life without an eid is made of sadness.