Hi!
I made some (imho) improvements to the OID implementation, if someone with write access would find time to review/commit the attached package, I'd be grateful.

The commit message:
Make OID implementation more compatible with the description in http://docs.mongodb.org/manual/reference/object-id/.

- Use the UNIX epoch instead of Smalltalk epoch for timestamp part, store BE so it's pseudo-sortable by time (also, you can use getTimestamp() in mongo shell and get a sensible value)
- Use a per-session ID instead of localhost name for machine identification. localhost name is far from unique on some platforms (always 'localhost' on Macs), better with a unique ID per image session.
-  Counter initialized with a random value.

As an added bonus, [OID new] bench should see a ~10%  increase in performance.

Cheers,
Henry