Rewrite dbd to use CNID IPC instead of opening the db directly

Rewrite dbd to use CNID IPC instead of opening the db directly

In order to fix buf #447 (race condition between dbd and cnid_dbd)
dbd must be converted to work over the network IPC channel with
cnid_dbd instead of directly working on the BerkeleyDB CNID database.

Add CNID db IPC command for wiping the db