New dn2id format with base/one/subtree indices (ldbm/bdb2)

New id2entry (id-less) format (ldbm/bdb2)
Removed id2children (ldbm/bdb2)
Added nextid database (ldbm)
Broke ldbmtest
Removed ldif2* tools (ldbm/bdb2)
Added slap tools (slapadd, slapcat, slapindex)