Changes by: Jason Hickey (jyh at cs.caltech.edu)
Date: 2006-03-16 14:59:25 -0800 (Thu, 16 Mar 2006)
Addressed bug#533, where Omake_cache.is_dir was computing digests.
Now a node can be in a "PartialStats" state, where the Unix.stat
information has been computed, but the digest has not.