Exposing file system access by extending Waldo variables and performing writes based on their values.
We distinguish two types of objects during the course of completing a
commit.  The first is a priority object.  We will run complete commit
on all of these before running complete commit on the lower priority
objects.  The reason for distinguishing objects into high and low
priority tiers is that some objects may wrap additional data.  For
instance, a folder map object may wrap many files.  At commit time, we
want to serialize the changes to a variable so that can replay those
changes on the file system.  However, for this to work, we need to
ensure that the folder object is complete_commit-ed before any of the
subfiles are.  (Added separate priority mechanism to schedule complete
commits.)
Added a Waldo extension that makes changes to snmp backends when completing the commit.
Merged extensibility branch: should make it easier to subclass waldo types to extend their functionality.