Backend API

[luca regini]

After browsing and looking at the source code i find very difficult to 
understand the meaning of the following hooks:
  bi_extended
bi_entry_release_rw
bi_chk_referrals
bi_acl_attribute
bi_has_subordinates
bi_connection_init
bi_connection_destroy.
 Also what is the purpose of the tool hooks.
 I am looking at the 2.1.12 source.
 Thanks
Luca