bridge.py checks for the exisistence of /mnt/sd/arduino/bridge/ if found it imports mailbox_dbm as mailbox rather than mailbox.

mailbox_dbm uses anydbm for presistant storage of key, value pairs.

I am not entirely happy with this implementation but as a POC it is working.

ToDo:
reduce open/close operations in each get/put/delete to single open at init of mailbox_dbm

modified:   bridge.py
new file:   mailbox_dbm.py