mongodb/mongo — pull request #837 by esmet (2014-10-24 01:27:45+00:00)
Title:  Pass the old record to the storage engine's updateRecord function.

Now, any updateRecord implementation that needs the old record
no longer needs to do a read-before-write. One such implementation is
in KVRecordStore, which uses the old value size to calculate a size
delta that is stored in a metadata dictionary.

https://jira.mongodb.org/browse/SERVER-15793

All unit tests pass and so do the core js tests that start with 'update' (ie: jstests/core/update*'