fix missing expect() call in password-tests

add a console.trace that helps debug it
Handle modifications to EJSON custom types

OplogObserveDriver cannot try to directly apply these
representation-level mutations; it needs to get the entire custom type.

This implementation is overly conservative, but in practice
Meteor-originated writes shouldn't mutate EJSON custom types
anyway (they should treat them as atomic).
Test changing Date and ObjectID